There is already a thread for beginners to chat in in the 「日本語の勉強」 (Nihongo no benkyou) section of the forum.
For that matter...
your sentence would probably be (私の)おならは小さいです。([Watashi no] onara wa chiisai desu.). "Watashi no" is in parentheses because it's optional. And "onara" is the more commonly used word for "fart". "He" is a more...formal term for farting, like the word "flatulence" in English.
But anyway, next time, please post in the beginners' thread in the 日本語の勉強 forum if you feel like chatting.