Guide me please!

[hyxfei]

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.

can i set a blog in wordpress.com with same contents in blogger? what's the difference between blogger and wordpress? just more functions in wordpress?

yes you can gie same content but what benefit you will get if you make two different sites in different platform then better to maintain uniqueness.

May be this way can create some traffics too, if one of our blog site didn't work properly, we still can earn in another blog site. Later if we find out which blog is generating the most traffic then only we drop one of it, do you all think this way is good?

But this is the wrong way just think of one way as your articles will be same and from search engine people come to one of your blog ,you can't waste your time for 2 sites you may post different articles then some chance will be there.

yes. you can hold two different bolg for different articles and even this way will earn more than together published them.
many people like to visit specific blogs than mass.