Here is a little more info to add into from my Sensei which I find quite useful:
±± Ninja ±±
A ninja is someone who uses their full abilities in the service of his/hers beliefs, working to achieve a goal. This goal can be anything from peace to war, money, destruction, personal griefs or even revenge and can be shared with others or individual. Most ninjas are fighters and correspond to the bulk of the military force of the great nations. However, a ninja doesn't need to be a fighter. Even medics or a simple carpenter may, in times of need, use his abilities (medical knowledge or abilities in working with wood for example) to accomplish the goals he set to himself, following his beliefs.
±± Chakra ±±
Chakra is the energy that is formed through the passive combination of both the Physical and the Spiritual energies in a sentient being. Physical energy corresponds to the vitality of the body and its own energy. Spiritual energy corresponds to the mind or spirit, and comes from the awareness and "soul" of each sentient being.
Some ninjas have high levels of chakra because they have great physical energy (like the Akimichi or even Tsunade) and others because of their spiritual energy (like the Uchiha and the Yamanaka). However, its much more difficult to increase the spiritual energy than the physical one, thus why all ninjas pass through intensive physical workout.
±± Ninjutsu ±±
Ninjutsu, or Ninja Arts, is the ability to, through the use of chakra, accomplish tasks that would be otherwise impossible to do. Ninjutsu are done by molding the chakra and using it to produce the desired effect/technique. This is done by two basic principles: Shape and Nature Manipulations. These correspond to the two broad areas that one needs to change in the chakra to produce a jutsu. Shape manipulation pertains to the ability to give your chakra a desired form while Nature manipulation pertains to the ability to give your chakra a desired set of characteristics/properties. Sometimes, to better mold chakra, ninja use Handseals. Handseals are simply hand gestures that allow the ninja to more easily concentrate and mold the chakra into the desired technique.
±± Genjutsu ±±
Genjutsu, or Illusionary Arts, unlike ninjutsu, don't produce a real, palpable, feasible effect; it produces an illusionary effect. With a specific KG however, the illusions can become so strong that the body will be fooled into mimicking in real life the fake effects its perceiving through the illusion. There exists two types of Genjutsu: the passive, non chakra fueled ones (basically illusions to our senses like visual paradoxes and such which have little use in the RP and can be easily overcome through experience and logic) and the active, chakra fueled ones. Within the active chakra fueled ones two subtypes exist: Dojutsu fueled Genjutsu and Normal Genjutsu.
Genjutsu works by using chakra to disturb the chakra flow of the opponent, specially in the brain, altering his senses. By doing this you can make him perceive any thing his senses are capable of: pain, heat, cold, tickles, iching, etc etc. A ninja can make the opponent taste, smell, feel, see or hear anything he wants. However, because this is done by using your chakra to manipulate his chakra flow, the ninja needs to be close or, many times, have direct eye contact or even physical contact. This is the main limitation of Genjutsu: range. The further you are away from your opponent, the harder it is to induce the fluctuation on his chakra flow to produce the genjutsu.
How exactly does it work? Well, every one has a balanced chakra flow. The chakra flows in a balanced combination of both physical and spiritual energies. The ratio between them vary from person to person (that is how each person has a different chakra signature) but its always calm and balanced. To produce a genjutsu, a ninja uses his chakra to disturb that balance in a controlled way. A fluctuation is created in the persons chakra "wave length" and makes it fluctuate in a given way. This produces the illusion by scrambling the users link between his Spirit and his Body which effectively is the link between his mind and his senses. To make your chakra be capable of doing the correct fluctuation, you need to use, most of the times, handseals. These help you mold and shape and focus your chakra to the correct wave length you want to induce, thus enabling you to use it to disturb the targets chakra flow.
±± Taijutsu ±±
Taijutsu is basically Hand to Hand combat. Its composed of several disciplines and arts, the most used of which is called Strong Fist. Other types include for example, Gentle Fist. Taijutsu uses the body as a weapon to attack or defend against your enemy. Its powered by chakra but in a different way than Ninjutsu or Genjutsu, as you don't need to mold chakra to perform Taijutsu (as seen in Rock Lee's case). Chakra in Taijutsu acts as the fuel, powering the body through its moves, specially in terms of Physical energy. The main characteristic of Taijutsu is that it can be combined with several other areas of a ninja's arsenal, such as Kenjutsu or Ninjutsu (in this case producing Nintaijutsu). This makes Taijutsu the basic skill every ninja has to have.
Taijutsu can be advanced through mastery of the Eigh Inner Gates. These are "limiters" that exist within the chakra circulatory system and that regulate and limit the chakra output, keeping it at safe levels, thus keeping the body safe. Through intense training and skill, a ninja can unlock them gaining access to increased chakra output and, through that, increased physical power. However, doing so damages the body and may even lead to death.
±± Kenjutsu ±±
Kenjutsu or Sword Arts, are the skills regarding the use of swords in battle. Its in essence a more advanced variation of Taijutsu in which you use a bladed weapon (sword) to increase the letal capability of your attacks and to increase your defensive ability. Sword Arts vary greatly, perhaps even more than Taijutsu, and can, as the former, be combined with Ninjutsu or Taijtusu to increase its abilities and power.
±± Fuuinjutsu or Sealing Arts ±±
Fuuinjutsu or Sealing Arts, are a type of Jutsu that seals chakra, living beings, objects, energy, etc whithin another object through the use of kanji codes/spells.
Fuuinjutsu may vary greatly but most obey the same basic principle: You need a medium (living or not) in which was prepared the Kanji Codes/Inscriptions of the seal. You need to expend chakra to activate the seal and chakra to sustain it for a given amount of time. To release it, you must once again expend chakra to unlock the seal, while still needing the correct "key". The "key" is a variation of the technique only known to those who create it, thus disabling the probability of the seal being released by someone else; it can be a given set of handseals or even a DNA imprint (through a blood contract). However, even if most seals may work in this simple fashion, some more advanced seals work in many other ways. Even if you take into account that all seals must be triggered/fueled by chakra, they must all have a medium in which to seal away the target.
Because seals are fueled by chakra, they become weakened through time, as the chakra that was expended to create and maintain it, becomes consumed. Because of this, when sealing something in a living being, the seal is generally made to use the chakra from the being to sustain itself, delaying the eventual weakening.
±± Gogyo/Godai or The Five Natural Elements ±±
In Narutoverse exists 5 main energies in Nature: Fire (Hi), Earth (Tsuchi), Wind (Kaze), Water (Mizu) and Lightning (Raikou). Fire represents rebirth; destruction as a means for creation and emotions. Earth represents resilience, strength and durability; stability and bounds. Wind represents freedom, absence of regret and freedom of spirit. Water represents tranquility and peace; life and nurturing. Lightning represents wildness and boldness; its the element that embodies the desire to break free and to rebel.
±± Godai Seishitsu Henka or The Five Elemental Ninjutsu ±±
Elemental Ninjutsu correspond to the ability to manipulate or use the basic 5 elements for Nature through Ninjutsu, more specifically through Nature Manipulation. These correspond to 5 releases or styles: Earth Release (Doton), Fire Release (Katon), Water Release (Suiton), Lightning Release (Raiton) and Wind Release (Fuuton).
Each of these releases has a weakness and a strength towards another element:
-Fire Release is weak against Water Release and strong against Wind Release
-Wind Release is weak against Fire Release but strong against Lightning Release
-Lightning Release is weak against Wind Release but strong against Earth Release
-Earth Release is weak against Lightning Release but strong against Water Release
-Water Release is weak against Earth Release but strong against Fire Release
Any questions?