If you don't have a product or service of your own, how can you use Twitter and Facebook to promote other people's products? All I ever find is advice on promoting your own business.
Do you mean CPA or something like clickbank products? I use twitter for marketing a bit myself, but generally speking especially with twitter you wan't to get them onto your mailing list as fast as possible. Because people stop using twitter(normally at least) after a couple of months. It isn't that important when you promote CPA offers. As you don't need to convince them so much to fill out something where they doesn't have to pay for it as with a clickbank product.
See, people don't go to Facebook or Twitter to spend money so don't ever try to push clickbank offers there. It won't sell and even if it does; conversion will be much much lower than what you expect. And this is the prime reason why you are told that go and create relation there. In my opinion these are the Goldmines if you want to create email lists and trust me these places are super fast for it and later on you could push these guys via follow up mails to convert handsomely. If you don't wanna create email lists then go for CPA as "onetouch" suggested because these offers (i am talking about email/zip submits only) don't cost a penny to the users and that's what the mindset is of visitiors of these sites. Hope it makes sense to you. Let me know if you need any further help. Take Care