I want to know that how we can earn on internet

Ebay?

Learn how to code
Come up with a good idea for a site
Learn about SEO
Learn about internet marketing
Buy some server space and expieremnt
Sell products/services
Start working for a compnay that's internet based to learn the ropes
When all else fails, there is lots of money in porn

How do you you want to earn money? Do you have a business idea in mind? Do you want to sell a service or product? How much do you expect to earn? Do you want to be global? National? Local? All this will effect your ROI.

You will need a website/page that has good call to action.
You will need to market that site via SEO, SEM, Classifieds, PR, networking (Online sources) as well as Offline sources, (print, classifeds, broadcast, TV etc... )