u cant earn only by adding posts ..you have to create some ad zone on ur blog where u can show the advertisement, and if some one click on it u will get the money,
what to do for showing the ads on my blog?
ans..for showing the ads on ur blog u have to join some websites of advertisements such as adbrite.com or bidvertise.com etc. then there u can create ur new ad zone. ther e are some steps . the last step is to copy html code paste it on ur blog.
copy it and then go to ur blog in blogspot.com and go to layout add the gudget (html script) and paste that code.and save it
the company which find that ur zone is suitable for their ad they give the advertise on ur blog and then u can earn..