An auction decides which ads will appear with each specific search on Google. It also determines the order in which ads will be placed on the results page (or if any ads will be shown at all).
When a search occurs:
Google Ads will find all relevant ads based on keywords
Google will then cull the list of all ads that aren’t eligible (such as ads targeting a different country)
Then with the remaining ads, the ads with a sufficiently high Ad Rank will be shown.
