Can I really earn money through affiliate marketing?

There are many people on the Net who are dying to help us with earning huge cash doing affiliate marketing – all of them of course charge for their service. But I wonder if I can do it without resorting to them. Something like building up a WP site of my own, setting up one or more affiliate products, and then promoting them.

Question is – will the venture be worth the efforts (seems it’ll take lots of efforts)?