±± 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 (every living being with a conscious mind has chakra). 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.
Yin and Yang are based on this same concept. Yin is the basis of the spirit while Yang the basis of the body. In this i won't go into more dept because there are 2 things to consider: Yin/Yang manipulation in our RP is different from the manga one and both are more or less inacessible.
Chakra flows in a circulatory system inside your body, in a way that much resembles the blood circulation. This circulatory system has 8 small reservoirs that act as both storage but also chakra regulation. These are the eight inner gates. Along your circulatory system, small "portals" exist that enable you to expell chakra from your body. These are called Tenketsu and there are 361 of them scattered allong the body. When a tenketsu opens, chakra poors out of it. Its by molding the chakra that comes out of the tenketsu that you produce ninjutsu and genjutsu.
±± 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 2 stepts: focusing your chakra and molding your chakra. Focusing is using your will power to "will" a portion of your chakra to do something. On the other hand, molding is giving your chakra a set of characteristics that will enable you to produce the desired end effect.
Think of the chakra flow as our breathing. Normally, it happens passively, without any conscious intervention. However, when you need to you can use your will to control it. Its the same with your chakra flow. Its happens normally without your consicious intervention. However, you can focus your chakra and make it produce something.
Now, molding the chakra is done by two basic principles: Shape Manipulation and Nature Transformation. 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 transformation 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.
±± Elements ±±
Lightning is a very violent and sharp element, capable of paralyzing and burning our opponents. It is considered to be the fastest of the basic elements. It's generated by its molecules being forced to move at a great velocity which causes it to be unstable to a degree. Lightning is weak against wind, as I will explain in detail in the wind section, because wind is a natural insulator while it's very strong against earth, being capable of destroying it and crumbling into pieces. It's a very good combination with water because it electrocutes it, while it's neutral to fire because of reasons I explain in further detail.
Earth is a versatile element because we walk on it and it's everywhere around us. Mostly everywhere you walk, you will be able to use earth techniques, which gives a great advantage against water users when battling without nearby water sources. It is a solid element with great crushing and piercing characteristics. It has a tremendous amount of applications thus why it has the most techniques. It's projectiles possess a great force because of their mass and it's proportional to the increase of acceleration. It's simple logic. The faster you throw a rock the more it will hurt, lol. Earths' main weakness is lightning as mentioned above, while it's strong against water because it can split water waves, redirect them, push them back, etc. Mass is the key. It's a great combination with fire because, as mentioned, it turns it into lava or in case you have mud, it hardens it. And as I already said, it has it's unique applications in conjunction with wind.
Water is a liquid element and can be found anywhere in our world. I won't go into specific numbers but you're aware that a lot of stuff is made of water or has water in it. This makes it a very versatile element, the second most versatile actually. Water is strong against fire because of its extinguishing power, but it's weak against earth because it can't break it down and it only makes it wet. Note however that in some cases water turns earth to mud which can be useful but also a double egde. Regarding the other two elements, water is very good in combination with both. Lightning electrocutes the water while wind gives it more force and makes it generally stronger.
Fire is a dangerous element, capable of burning stuff in the matter of seconds. It's a very violent element because of its destructive power. It's main trait is heat, which is the cause to melting and incineration. It's important for you to notice that fire requires oxygen to burn. Since oxygen is a part of the air we breathe, no air would mean no oxygen. The counterpart would be more air resulting in more oxygen and a stronger fire. However, there are a few scenarios for this and I believe your teacher will explain these to you in your training. It's weak to water because it's easily extinguished but it's strong against wind because it "eats" the air and the oxygen. It's neutral against lightning and since none are solids they pass through each other. Fire with earth is a good combination because it can harden mud or turn regular earth into lava.
Wind is the most versatile element in our universe because it's everywhere around us. Again, air is not a solid but using our chakra we can condense it into sharp projectiles, blades and such. One of its components is oxygen which makes the fire burn. The interesting thing here is the amount of wind (air) you put up to the fire. With a small amount you make the fire burn stronger and spread faster while with a huge amount of air you will put the fire out. Because it contains oxygen it is, unfortunately, weak to fire while being a natural insulator it's strong against lightning, capable of dispersing it and preventing its spreading. As mentioned it's a good combination with water because, for example, it gives a water projectile more thrust power and it speeds it up. This is also applicable to various ninja tools, so keep that in mind. Regarding earth, they're neutral but there can be some interesting usages. For example, picking up dust from the ground, small rocks or even making giants patches of earth float above the ground, and such.