Someone types "post construction cleaning Chicago" into Google. Above the regular results they see a few listings marked as ads. If yours is one of them and they click it, you pay for that click. Appearing in search costs nothing.
The price of a click is set by an auction that Google runs for every query. The ad with the better mix of bid and quality ranks higher: how closely the text matches the query, and whether the person finds on the page what they were promised. So an advertiser with a more precise ad and a clearer page can pay less per click than the competitor next to them.
This kind of advertising is also called PPC, pay-per-click, or contextual advertising, because the ad depends on context: the words of the query, and on YouTube and partner sites also the content of the page and the person's interests. In practice it usually means Google Ads, and that is what we work with. Other ad systems we connect on request.
How it differs from SEO and social ads
SEO services also bring people from search, but it takes months. Ads give you clicks on launch day and stop when the budget does. Facebook and Instagram ads show your ad in social networks to people who weren't looking for anything. Google Ads works with demand that already exists.