First and foremost, you need to reach a certain number of points before you are able to create your own jutsu. (see the Points System)
The jutsu you apply for under Jutsu Creation is expected to match your character's rank or be a rank below said character. For jutsu higher than your character's current rank, you'll need special permission, or it needs to apply to your Kekkei Genkai. For example, a Genin (D-rank) in the Sarutobi clan can learn C-rank techniques so long as he/she has the points for it, since the members of the Sarutobi clan can use jutsu that is a rank higher than their current rank.
S-rank Sarutobi ninja aren't able to simply create and be able to use SS-rank, that would still require administrative permission.
Once a justu is approved, you are responsible for creating a Training Thread with a word count dependent on the level of that technique. Feel free to title this thread whatever you'd like, but it must have [Training Thread] in the title to indicate that it is in fact a thread you're using to be able to utilize another jutsu.
Word-count requirement:
E-rank - 150
D-rank - 300
C-rank - 500
B-rank - 700
A-rank - 1000
S-rank - 3000
SS-rank - 5500
Bear in mind that until the above requirement is reached, you will be unable to utilize said jutsu in-character until your character's training is complete. Notify an Administrator when you've hit enough words for the training to be completed.