To make residual income online you should start up a blog on a topic you know a lot about.
Write lots of great blog posts that are very helpful and will solve someones problem. You can then sell E books with more information on a topic.
Or you can monetize your website with advertisements such as Adsense or media.net or other Adsense Alternatives.
You can also promote affiliate products or services on your website and earn money even while you're sleeping.
But first you must work hard to write that content and get website traffic.
After you work really hard in the beginning you can then start to produce an income without working as much.
You'll still need to work on your websites but you won't have to spend as much time working on your website or blog as you did in the beginning.