When a user enters a search query on Google.com, Google scans keywords on each webpage in its index to see if that page matches the user’s query. Google then displays the webpages that most relate to the word or phrase entered in the query.
Google also displays ads in response to search queries. But with ads, Google scans the keywords that you’ve chosen to represent your business. When a user searches for keywords you’ve selected for your ads, your ads can appear next to the search results.
Ads on Google search results pages are available on a cost-per-click (CPC) basis. This means that you’re charged only when somebody clicks on your ad and visits your website. Google also offers pricing on a cost-per-1000 impressions (CPM) basis for site-targeted campaigns.