Here is the opposite of there. There is another place, but here is where you are right now.
When someone yells, "Come here! Come here!" they want you to come to where they are — here means the present location for the person using the word. Unless you're in the same place, here is a different place for you and for someone else. People use here to indicate a specific place, like "See this scar right here?" There are also expressions like "here and there" (meaning all sorts of places) and "the here and now" (the present time).