If you're just geatting started, there's a simple formula for you to understand how to earn money with google adsense:

Revenue = Traffic * CTR * CPC

You probably understand what traffic means.

So CTR is Click Through rate, and it means how many of your visitors are clicking ads. It actually depends on how your site is adsense-optimized.

CPC is Cost Per Click. Different words have different costs. Some can be about $0,01, some are over $10.