There are really many different ways. In a nutshell:
-Work for an established company (lots of options, check out www.athomeopps.com)
-Start a blog or website, earn through ads or affiliate links
-Sell things you own or things you buy to sell (sell through e-bay, amazon, your own website, etc...)
-Sell things you make (etsy.com is a good starting place)
I have used all of these options actually, I have blogs, do freelance writing, have worked as a at-home customer service rep, sold on e-bay and etsy, just to name a few. I would suggest you do the same. It takes a while to get websites and blogs to the point where they are earning decent income and it can be difficult to make money selling things. In my opinion I would say find an online job (customer service, transcription, writing, whatever you want to do-again www.athomeopps.com lists these) and then start a website or blog writing about things you know, and if you're crafty maybe sell things on etsy. This way you have options, and hopefully a steady stream of income.