Welcome! It's best to look around the forums and find out what to post in different categories. Some are pretty self-explanatory (eg. Suggestions For POTCO), but it's probably a good idea to look around, to avoid putting things in the wrong place. :P
To get to your user settings, if you would like to choose an avatar or edit your profile, all you have to do is click on User CP on the homepage (use ctrl+f if you can't find it), and it'll take you to your toolbar. The first things you'll see are a message telling you that you haven't subscribed to a thread (you can subscribe to threads to get notified when something is added to a thread) and a message about reputation. You will recieve reputation if someone decides to rate one of your posts if they think it was helpful or they just liked it.
The links on the left are obviously what they say they are (no tricks here!). If you want to get to your profile, click on Your Profile near the top of the links. To edit your profile and show how artistic you are, click on Customize Profile two links down from Your Profile.
If you want to start making friends, you can click on Contacts and Friends, under Networking. Just type in a member's name to make friends or Contacts with them. Making a Contact doesn't send a friend request, but it works in a similar way. You can see when a Contact or Friend is online easier, in its own list on the homepage.
I expect Captain Del will come and talk you through group memberships and guilds soon, so I won't tell you about that so as not to spoil his Del Time With Newcomer.
Well, those are the basics. There's still a lot more to discover, and I expect you've noticed that you can pay to have a user page, signature, more PM space and more. The prices are listed on the homepage.
More site info in the below links:
Rank Images 101 and Colored Names
Screenshot and Image posting guide
Site Policies and Disclaimers
Site Moderators
Feel free to ask me or anyone else on the site any more questions you might have, because I haven't quite covered everything there is to know here.
Once more, welcome aboard! I don't think I need to warn you about the insanity that lurks in this place...