If you have a good product and want others to sell this for you, then you need an affiliate program. However if you don't have a product or are selling products for others, then the is no need to have an affiliate program.
Perhaps some further reading of these forums and others will give you a good idea of what you need to know.
Offhand you'll need software for tracking, book keeping help for paying the affiliates, shipping software for getting products out, affiliate manager to handle affiliate questions and inquiries, marketing manager to help with marketing, perhaps a network to help get your product out etc.
As eljefe3 said, it is a huge effort to build an affiliate program from the ground up. You may find it more advantageous to simply join the merchant program for an existing network, where they have all the tracking etc in place already.
[edited by: Drastic at 6:29 pm (utc) on Mar. 14, 2006]