First take a deep breath, and relax.
Next, click "my account" at the top of the page.
Under the second heading ("Your Account") click on "Your Profile."
Fill in a short bio in First or Third Person, and then fill in the other sections with whatever information you feel comfortable giving. I tend to be a bit of a paranoid, so I didn't fill out much else.
Set up Google Adsense and Google Analytics (I love Analytics, personally.) You can worry about the other affiliates as you gain experience if you want.
Pick a topic, any will do, write about it, and publish it--rinse and repeat :D
It may seem overwhelming, but it's not when you get down to it. Just break the big action into small parts, do them one at a time, and before long you'll be done.