well, you can start your free blog by register at blogger or wordpress.com, then start joining affiliates program like bidvertiser, adbrite and clicksor. You may also participate in to those paid to blog site like payperpost, blogitive and sponsoredreview.

But the main to earn online is still you have to promote your sites well, in search engines, or create lot of back links in forum and other blogger. It involves a lot of hard works.