There are metrics mostly about how much people react or engage with your ads, most famously, Clicks.

It is very tempting to become focused on Clicks as the most important measure of your ads, but you need caution here. Lots of evidence suggest that ads can work without anyone clicking on them. In fact, it is quite likely that more people who see your ad go to the website without clicking on the ad (they go via google search for example) than those who see the ads and click-thru there and then.