How costs are calculated
Every time someone searches on Google, Ads runs an auction to determine the ads that show on the search results, and their rank on the page. To place your ads in this auction, you set a bidding option in your account.
Most people starting out in Ads use the basic cost-per-click bidding (CPC) option, which means they accrue costs based on the number of clicks they get on their ads. If you use this option, the amount you're charged per click depends in part on the maximum cost-per-click bid you set in your account, also called maximum CPC bid. This represents the highest amount that you'll ever pay for an ad click. In fact, you'll be charged only the amount necessary to keep your ad at its position on the page.
A few other factors, such as ad quality, determine the exact cost of a click on your ad. But if you've set a maximum CPC bid of $1 for your ads, then the most you'll pay when a customer clicks your ad is $1. And if your competition bids only $0.50 for the same ad position, you'll only need to pay $0.51 to show your ad, assuming your ads are similar in all other aspects.