Google Adsense is a way to earn money through online content. You show ads to your visitors .and for showing ads google gives you money.
The ad that google show to your visitors is related to your content.
like if your content is related to your finance then Google shows ads related to the finance concept.
The Google AdSense program pays you in many factors like it the number of people clicks on an ad, ad impression, depending on the type of ad .
Your site also matters which type of content you have put online or the seriousness of the demand of content.
Many people ask the question do they have the right to show according to their choice this is not true because here google selects which type of ad will run on your site.
When demand and category match your content google show ads to your content. It is against the policy of Google to click on your own ads.
Many newbies asked do I have to pay for google to show ads then the answer is no google Adsense is free anyone can apply if it is fulfilling all the criteria.
Earning through google depends on many factors like the level of your content, where your visitors are coming from, quality of click.
Your potential earning depends on the type of content you produce like (entertainment, (arts & entertainment, finance, etc. Don't be discouraged if you don't get the results you want right away, factors like seasonality and currency exchange rates can also affect your earnings.
You will only earn when visitors perform an action. The revenue share of the publisher is 51% on the amount google gets to show the ad .google AdSense is dependent on many factors.