There are quite a few different names for facial hair, and it’s sometimes difficult for English learners to keep them all straight (to keep something straight = to remember something properly).
First off having hair only on the space between the upper lip and the nose is called a mustache.
If you have hair on the cheeks and chin it is called a beard.
If you have a mustache and beard, we usually just call it a beard. This is because people usually have both, so saying “mustache” and beard is a bit redundant. To emphasize that the hair covers the whole face (cheek, chin, upper lip) we sometimes call this a “full beard”.
If someone has a beard just on their chin, but not on their cheeks, we call that a goatee. Perhaps because goats also have long hair on their chins?
Side burns are hair that covers the cheek in front of the ears, they usually aren’t very big and often just look like natural extensions of the hair. The superhero “Wolverine” is famous for having thick sideburns.
If a man has no beard at all we say he is “clean-shaven.”
If someone has a bit of short hair on their face that you can see, but it isn’t long enough to be called a beard, we call it “stubble”.