First look for the Register button, there's one in the top bar, but you will also find a link just below the list of forums on the home page.
This will take you to the registration terms. Don't be put of by these, they are just the generic terms provided with the forum software, you are not signing your life away, just agreeing to use the forums sensibly and legally. Obviously read the blurb through and then agree to the terms with the button at the end.
The next page is where you put your details in. Choose a username which you will use to login with, it will also be used to identify you in posts and replies. It can be anything you like (within reason!), you will be told if it is already in use and given the option to choose another. Next down the list is the password. Ideally choose something different from the one you usually use, and you are asked to type it in twice to avoid a mistype (it is far less likely you will make the same mistake twice if you do make one!). The language and timezone shouldn't need changing.
Then there is a box to 'justify' your membership. This is simply to ensure that only people invited are allowed to join, so give a quick comment about who referred you to the forums, there's no need for a life history.

Finally you will get a confirmation of your application. You don't get immediate membership as a moderator has to approve the membership. Again this is simply to ensure that only approved people get access to the discussions here. You should get an email confirming your membership quite quickly. Depending on when you sign up it may be the following day though.