These advertisements are administered by Google and generate revenue based on clicks from visitors to the page and displays the same (impressions). Google uses their search technology to embed ads based on the content of the web page that you are visiting, the user's geographic localization (by IP) and other data such as previous search history on Google or visited pages by the user, their cookies, session length, operating system, browser used, etc..
It is also a method of putting advertising on a website with ads generally less intrusive than most banners and content are usually more related to the website where they appear.
Also, ads may be Google's product promotions or other companies or foundations like Mozilla Firefox also allows us to offer a search bar to your own website so that the user can search inside (the domain) or Internet searches if you do a search on the Internet with the search bar of the webmaster and the user clicks a sponsored link, some of that money goes to the respective account AdSense.
Google AdSense allows webmasters of all conditions, display Google ads relevant to the content of your pages to generate revenue for Google in exchange for advertising. The ads are targeted to what the user searches on their pages or related to the characteristics and interests of visitors according to their content and user data.
With the AdSense ads are the providers of those who pay Google for each click that a visitor clicks on an AdSense link presented on a website.
