Registering on the forum
Go to the forums.
Click on 'register', which are outlined by red in the 2 pictures.
You will see the above page, agree to the terms and you can continue.
Fill it in like it is filled in in the example: http://i.imgur.com/E7YFhae.png
Everything outlined by red shows you what you need to fill in, use different things than I used in the example.
If nothing went wrong, you will see the above page when you click 'Submit'. If something did go wrong, the forums will tell you what went wrong.
Check your email and click on the link in the email. This will verify your account.