There are quite a few ways to make money online, the one I like the most is affiliate marketing. Basically you advertise other peoples products on the net and sell them for a commission. There are ways to do it so it actually works out free. The best way to learn, though, is to be willing to spend a little on getting educated. If you're serious about making money online, it's worth it.
I wrote a couple of hubs about it, and I have a website with some great information.
Check those out for some more in depth information about affiliate marketing