If you are in the clan, you are able to ask for forum access if you have a site account. If you don't then make an account first! Now when you do that and are given the access, the first thing you should do is go to the New Members forum and post your introduction. This is mainly to tell people that someone just joined instead of randomly finding out which will still happen, believe me.
There will be a topic to tell you what you need to put in your Introduction topic in the New Members forum.