What is google AdSense and how to use it effectively?

I googled GOOGLE and got the following info on AdSense.

Google AdSense is a fast and easy way for website publishers of all sizes to display relevant, unobtrusive Google ads on their website's content pages and earn money. Because the ads are related to what your users are looking for on your site, you'll finally have a way to both monetize and enhance your content pages. Learn more about AdSense for content.
It's also a way for web site publishers to provide Google search to their site users, and to earn money by displaying Google ads on the search results pages. Find out more about AdSense for search.
The program is free, and combines pay-per-click and pay-per-impression advertising - meaning you get paid for valid clicks on the ads on your site or search results pages as well as impressions on your content pages. So go ahead and try this program. If you comply with our program policies, just complete our online application and select either or both of AdSense for content pages and AdSense for search. One application gets you approved for both AdSense and AdSense for search - you can decide to use any combination of these products on your pages.
We'll review your application and follow up with an email within 2-3 days. If you are accepted into the program, you can log in to your new account and get the HTML code to insert into your webpages.
Keep in mind that participation in AdSense requires you to have a website. If you don't have one, you can sign up for a free blog at www.blogger.com or create and publish useful, attractive webpages using Google Page Creator, at pages.google.com.
Hope this helps.

I'm doing this now, and in my case, you are using Google to direct people to a site, where they get to know a product, and purchase from that site.

Essentially what you're doing is advertising for a company, be it yours or someone elses. Needless to say, you get a heck of alot more exposure this way.

More if you need it.