What it means
Click-through rate is clicks divided by impressions, written as a percentage. It measures one thing only: how many people who laid eyes on your ad found it interesting enough to tap.
Why it matters to a small business
It separates a message problem from an audience problem, and those need opposite fixes. If almost nobody clicks, the picture and the words are not doing their job. If plenty click but nothing comes of it, the ad is fine and the page they land on is the problem. Without this number you end up rewriting the ad when you should be fixing the page.
Your ad was shown 4,000 times and got 60 clicks.
60 divided by 4,000, times 100
1.5%. Useful mainly as a comparison against your own other ads to the same audience, not against somebody else's screenshot.
The bit people get wrong
Click-through rates are not comparable across places. A rate from a search ad, where somebody typed your service into Google, and a rate from a feed ad that interrupted a scroll are two different measurements wearing the same name. Comparing them tells you nothing at all.