With CPA Marketing, all you need is an offer and traffic. 99% of the time, you don't even need a website to host the offer, as the company themselves will host it for you and just give you an affiliate ID to include in the URL. That frees you to focus on driving traffic to the offer.
The traffic can be ANY targeted traffic that you can obtain, using any of the myriad of traffic generating techniques out there. The more targeted the traffic is, the better the chance that the prospective customer will take the appropriate action to generate a commission for you.
If you're someone who understands web hosting, HTML, SEO, and various other technical aspects of internet marketing - you can make a great income doing this. The more you can do to generate high quality, targeted traffic - the more commissions you can make!