*the pleasant scenery you thought you were in fades away to reveal a generic creepy forest; dead trees, cobwebs, crows, all that. A cloaked man with piercings steps out from behind a tree, locking eyes with you*
Hmm...you look vaguely familiar. Maybe we've already met? That aside, you being here means you want to learn the illusionary arts. I hope you've prepared yourself mentally for this, the focus here is deception. Before we begin i need you to tell me all you can about Genjutsu.
*he leans with his back against the tree, arms crossed as he awaits your reply*
Creepy desolate environment??? *shrugs* This must be Orochimaru-sama's place
Welcome sensei. Yes we've met before. I'm surprised you recall that. I must be a memorable student eh? Anyways, genjutsu basically means illusion-ism. Sorta like magic, but with less pleasurable consequences. It is a form of genjutsu where a person utilizes chakra to distort the chakra flow of another person or creature. Due to the hand-in-hand relationship between an individual's chakra system and his/her physical health and condition, this distortion bears certain mental and physical effects on the target. Of course the effects are dependent on the particular technique used. Thus the simple idea of deceiving a target's mind by adversely influencing his/her chakra system- which is genjutsu- paves the way for myriad advantageous combat attacks.
Genjutsus can be cast in different ways: most requiring handseals, some don't, and some requiring no more than eye contact or finger pointing, or other subtle actions. I'm sure there are even some that can be cast by merely smiling (em sick cjs mehn xD). Basically what I'm trying to say is that the methods of performing them vary. All require molding chakra though.
Strongest genjutsus are arguably sharingan ones. The ones with the potential to cause most damage however are whatever a Kurama bio casts imo, as they can be made reality, literally bringing your worst dreams alive.
Dispelling a genjutsu requires two steps. The first, realizing the genjutsu, and the second, delivering the body from the effects. One must realizing the without metagaming. I believe one can use a combination of intuition and incongruities in an attacker's genjutsu casting to try to identify that he/she is in a genjutsu. This is mostly the headache of ninja who do not possess some kind of dojutsutu. Dojutsu users are able to see through certain techniques as their level of training permits. I'm actually hoping to learn more about this as I don't fall in the earlier group of ninja who do not possess dojutsu.
The second and equally tricky part of genjutsu "curing" is dispelling the technique from one's body. With this techniques of different strengths can be dispelled differently. Inflicting pain on one's self is one way of doing this. However the amount of pain required is proportional to the strength of the technique. Another method is by surging some kind of chakra through your body. This can be done using the famous gen release technique, kai, or some other technique whose effect is the emission of chakra from "all or most of your tenketsu at once in a less focused manner." It is important to note that other than kai, most available techniques may only work against genjutsu of lower rank. Finally, altering your chakra flow through the introduction of foreign chakra or energies. Here is where perks like Jinchuriki, SM and CM give an advantage.
Last but not least genjutsu can be layered provided it is done in the right way(higher one first then lower one).
That about sums up what I remember from the scrolls I been reading dear sir U_U