First of all you must have a site or blog rich in height quality content. Your site or blog must match Google AdSense policies for content, otherwise, you will not be able to earn and cash money with AdSense from it.
Second step is to promote your content. You must have some visitors on your site or blog in order to make profit advertising on it. As an example I must tell you that, Your gains are as big as your visitors financial power and their wiliness of buying things.
Now, it’s time to make a Google AdSense account. You must provide full and real data about you in order to accomplish that step. You will have some great tools for generating ads units and plenty information for placing thous on your site.
If you reach the $100 level of earnings you are at 1 month distance from your first payment received from Google.