Jutsu

Jutsu, or skills/techniques, are the mystical arts a ninja will utilize in battle. To use a jutsu, the ninja will need to use his chakra. To perform a jutsu, the ninja will bring out and release the two energies of chakra. By forming handseals, the ninja is able manifest the desired jutsu. Because of the extensive number of hand seals and different combinations, there are thousands of potential jutsu to be discovered.

The Basics
There are three types of jutsu: Ninjutsu, Genjutsu, and Taijutsu. There are also Kekkei Genkai abilities which aren't jutsu, but inherited abilities passed down through certain clans. Jutsu can also be attributed to certain parts of the body. (eg. Dojutsu is Jutsu of the eye.)

Ranks
Depeneding on the difficulty or skill necessary to perform a jutsu, they are ranked differently. There are six different ranks in jutsu:
 * E-rank - Academy student level: E Rank Jutsu are learned by Academy Students which are the basic and most fundamental Jutsu for all graduating ninja. (e.g. Clone Technique & Transformation Technique)
 * D-rank - Genin level: D Rank Jutsu are Genin level technique and can be achieved by all Genin, though many ninja only learn their "type" of technique. (e.g. Earth Release: Inner Decapitation Technique)

Kekkei Genkai and other unique abilities of users do not have a rank.
 * C-rank - Chunin level: C Rank Jutsu are based on Chunin level technique though some Genin can perform this and some Chunin cannot. (e.g. Fire Style: Fireball Jutsu)
 * B-rank - Jonin level: B Rank: B Rank Jutsu are Jonin level technique but Naruto can also perform this technique, emphasizing his determination and high chakra levels. (e.g. Shadow Clone Technique)
 * A-rank - Kage level or Jonin level: A Rank Jutsu are Elite Jonin level and up, even including some Forbidden Technique. Some Elite Jonin and Missing Ninja will create their own technique as their "Trump Card" or even forbidden one.
 * S-rank - Secret, extreme level: S Rank are Secret, high class level technique. Tecniques of this rank are mostly known to only 1 or 2 ninja and are often forbidden.