Explain how to earn money from Blogging?

[Wukong]

First you make your blog.
Then you allow others to advertise on it. They pay you for this.
Any time anyone clicks on one of the ads, you get paid for that too (called a referral)
Sometimes, you get a "kickback" if they make anything out of the referral.
Google, for instance, will help you set this up.

You can also get paid for endorsing, recommending, or writing favorable reviews of softwares or other stuff (as happens with on line magazines, for instance)

Basically, that's it.

However-
Another almost universally popular way - collect lists of the people who join your site, or harvest their details if they just go to your site, and then sell the list. (Even shops do that, if you ever pay by credit card)
Or you could just let "3rd parties" have access to your site and gather the details themselves, or track whatever visitors do or go. You can get paid for that, too.
There is a lot of cross referencing. Advertising companies build very detailed profiles this way.

Examples of organisations that harvest and sell/share your personal details with or without your permission are - Google, Chrome, Facebook, Twitter, almost all other social networking sites, thousands of blog sites, etc etc.
Sometimes I wonder why NSA and FBI even bother.