ETA: eljefe beat me to the post (and in the process reminded me to say "Welcome" - sometimes I forget that I'm not a newcomer here anymore). Along with his comments:
The simplest way to get your feet wet is to use a hosted service (like blogger - but that's not a recommendation, it's just the only one I know about). If you start that way, you'll most likely want to move to your own domain after you learn the ropes. The hosted services take care of just about everything for you, but they also tend to control a lot of things you want to control yourself if you're serious about affiliate or any other kind of marketing. If you decide to try a hosted service, be sure to read all of the fine print before signing up - some have strict limitations on the kinds of advertising you can use.
If you don't like the limitations of the hosted services, you'll want to learn more before you start. Try dropping in at the "New to Web Development" subforum - you're likely to get better answers to newbie questions there. (ETA: In addition to following eljefe's suggestions - I think I'm going to read some of those gems myself.)
[edited by: Beagle at 2:06 am (utc) on July 10, 2008]