Now are you asking how to make money being an affiliate marketer or what does an affiliate marketer do?
I agree with what manogua said steps wise. But I would start with finding a niche/ or group people you want to target first. I would stay away from the big markets like health and money making niches cause those will be hard for you make money in if you are just starting out. What kind of marketing experiences do you have? What niches, hobbies, or things that interest you would be a great starting point. Also what kind of promotion do you plan on using (social, ranking websites, email marketing, PPC, etc.)??? Providing us with some more info would help out a lot to guide you in the write direction. When I first started affiliate marketing many years ago I used Clickbank. Best of luck to you buddy.