to become a Chunnin there are a few things you need to do
1Must be atleast level 20
2Must have at least 2 jutsu's
3Have fought at least 1 official match
4Must have 1 element
then
4 Sign up here
5 Awnser the 2 questions that you get in your class(thread with your name will be created once your signed up here)
6 Awnser the 3 a bit harder questions that you get in your class(thread with your name)
7 take the Chunnin test, pass
And you'l succesfully become Chunnin