Here is what Google writes about it’s adsense program:
“Google Adsense is the programme that can generate advertising revenue from each page on your website—with a minimal investment in time and no additional resources.
Adsense delivers relevant ads that are precisely targeted on a page-by-page basisto the content people find on your site. And when you add a Google search box to your site, Adsense delivers relevant ads that are targeted to the Google search results pages generated by your visitors’ search request.
You can customise the appearance of ads, choosing from a wide range of colours and templates. You can do the same with your search results page. Your reports are customisable, too. Flexible reporting tools let you group your pages in any way you want so you can view your results by URL, domain, ad type, category and more to learn where your earnings are coming from.”