Hello @PamG035 ,
Opens are when a contact opens an email you've sent them. This is tracked by a 1x1 pixel invisible image being downloaded / shown in the email at the time of opening.
Clicks are when a contact explicitly clicks a link in your email. These are tracked by the original links you insert being automatically rewritten, with tracking coding at the time of sending. When a contact clicks the link the tracking coding will redirect them to the actual link, while it reports back to our system.