A lot of sites make out that you can make thousands with little to no effort on your part - this is not true - as with any job, you get out what you put in, and there is money to be made on line either through affiliate programs, online paid surveys, blogging, ebay, AdSense etc. I would say that affiliate marketing produces the most income but also requires the most time and effort. There's a good site that describes the various ways to make money from home here.
One thing I would say though is if anyone asks for any money to show you how to make money online - don't pay - the information is freely available from sites like the one I've linked to, you just need to invest a bit of time into doing your research.
Hope this helped.