Basically, you pick a profitable niche for your online business, and then you find an affiliate partner who has products available in that niche. Some of the most popular affiliate sites are Clickbank.com, Amazon.com, and CJ Affiliate by Conversant (formerly Commission Junction). Between them, they offer just about any digital information product (like ebooks, audio files, video files) or physical product you can think of. May big name companies and brands, like Wal-Mart, Home Depot, etc. run their affiliate programs through these third-party affiliate sites.
Get-rich-quick schemes and fad weight-loss diets are naturally popular because they satisfy the id while also attending to the super-ego. The ego's job is complete when it sees something like this. The appeal of "fast'' stems from the innate desire for instant gratification, so beware of what seems too good to be true (they often are) when you're looking to make money quickly. Be wary. Listen to the conversation deep within the confines of your mind and do your best to tame the proverbial beasts.