Google has a long history of running ads in search results, but with the advent of AdWords, the company has made it easier than ever to target ads to specific segments of users.
AdWords is now the default in all Google Apps and Google Search.
Advertisers who have a Google account can target ads in the Google Apps for Business, Google Search and Google AdWords for Business groups, but if you’re not a member of either group, you’ll have to opt in to receive ads in those groups.
Google Ads is a good place to start.
How to opt-in to Google Ads