"Hehe.... you're funny, sensei" xD
Chakra:
Chakra is the energy formed by combining the spiritual energy and the physical energy present in our body. It is the base ingredient to most of the technique performed by a shinobi/ninja like ninjutsu, genjutsu, taijutsu etc. One would die if he/she is depleted of the Chakra in their body. With the correct control and balance on one's chakra, one can perform impossible feats compared to actions done without the usage of chakra.
Forms of Chakra:
a) Raw Chakra which is readily present in our chakra circulatory system of our body.
b) Elemental chakra which is slightly more advanced, since it is formed as a result of the nature manipulation of one's raw chakra. These chakras mostly have elemental properties of earth, water, lightning, wind or fire but in some rare cases two or sometimes even three elemental chakra are combined to create new elements such as wood which is a combination of earth and water, or Lava which is combination of earth and fire element.
c) Natural Chakra/Energy - They are present in the terrains all around us.
Handseals:
Handseals are certain actions performed with one's hand in order to control and balance the Chakra while using certain techniques. There are twelve basic handseals based on the Chinese Zodiac animals. Different set of handseals are used for different techniques, especially ninjutsu and genjutsu . Some ninja/shinobi after mastering certain techniques to a very high degree, can perform them with fewer or even without the use of handseals.
Genjutsu:
They are a set of techniques used by ninjas specifically to deceive their opponent by manipulating the flow of chakra in the victim's brain. Unlike the ninjutsu and taijutsu, which effects the opponent physically, Genjutsu effects the opponent's senses (or mentally) and thus misleads the opponent to believe in non-factual happenings around them. Genjutsu, in most cases, are also used to inflict damage or paralysis upon the victim by making them believe that they are being hurt in some manner. Another use of genjutsu is for interrogation purpose to obtain certain information out of the victim.
Ten prominent users of Genjutsu:
1. Itachi Uchiha.
2. Shishui
3. Sasuke.
4. Madara
5. Obito
6. Kurenai
7. Fukasaku and Shimu
8. Second Mizukage
9. Danzo
10. Tayuya