Swimming and snorkeling are two different things. Snorkeling is the basic skill of free diving. People who can't swim can also play snorkeling after training. For people who can't swim, snorkeling is mainly floating, that is, floating on the water surface and watching the underwater scenery.
So whether you can swim or not, you need to immerse your head in the water for a long time. You can watch the underwater world with your snorkel instead of breathing.