when a driver makes a pit stop, they leave the track, briefly stop for their mechanics to replace their tires (or sometimes replace a busted front wing or somehow patch up another damaged part/make a quick adjustment to their wing set up), and then rejoin the race. Currently all drivers are required to use at least 2 different types of tires during each race, so that means everyone needs to make at least 1 pit stop to switch tires. so the race itself doesn't stop, but everyone has to make a stop at some point! when you do it is up to your team's strategy, and that's one of the biggest elements of f1 racing - how teams will handle the pit stop(s) and tire choices! at some tracks it makes more sense to do 2 stops because the tires wear out faster, but as each pit stop tends to add about ~20 seconds due to the time it takes to slow down, stop, and get back up to speed, teams might try to make it through on only 1 stop if they think they can keep the tires in good shape... but that might backfire if their tires degrade too much, so it's a tough strategy call. And the choice to pit at different times in the race can make a big difference too, for a lot of complicated reasons - there are way more factors than i can explain over the top of my head, but i'm sure there are helpful vids on youtube!