Over is a weird word, it's heavily overloaded with a lot of different meanings, and there's no easy way to know other than context.
It can mean on top of and covering. The plates are over the placemats.
It can mean done or completed. The event is over.
It can mean you have to climb something to get to something else. The house is over the hill.
It can mean "greater than". Over 2 hours I waited.
It can mean "get out of the way", often implying lateral movement. I asked him to move over.
It can mean "come from out of the way or a far distance". Come over to my house.
Phrasal verbs/well-known phrases: to go over means "to examine in detail", hung over - what you are after drinking a lot the next day, take over - to assume ownership of, authority of, or to conquer, etc.
Here is a lot simpler, it just means "where I am."
You can even say come over here, please. to mean "come (from a far distance or out of my way) to where I am, please."
Come over is a very common phrase, as is move over, you can basically memorize these as equivalent to come here and move away.
And it is entirely possible but somewhat rare for move over to mean "move (from a far distance or out of my way) to where I am, please", but this will almost always be said as move over here or the person will be motioning toward you if they mean for you to move near them.
In Come over here and Go over there, the word *over* effectively means *away from* (wherever the speaker and/or addressee are currently), so it's not really "necessary" in either of my two examples. But just as the single word *here / there* on its own can imply *over here / there*, so we often just use *over* to mean *over here / there*. – FumbleFingers Reinstate Monica – 2018-05-21T12:20:05.953
Thus you might phone a friend and say *I'm bored. Can I come over?* (meaning *over to your place, away from "here" where I am now).* But equally, you might say *I'm bored. Can you come over?* (meaning *over to my place, away from "there" where you are now).* – FumbleFingers Reinstate Monica – 2018-05-21T12:24:51.617
@FumbleFingers That looks like a very good answer to me (might be worth pointing out that over and here are both prepositions). – Araucaria - Not here any more. – 2018-05-21T12:59:42.743
No one I know says "Call her here" for: Tell her to come here. And again, we are off topic re the OP's question, where "Call her here"is simply wrong. The question was: what is the difference between over and here, which I think I answered. – Lambie – 2018-05-21T21:16:46.870
Call her here makes it sound like her is a dog, small child, or someone/something expected to obey. – LawrenceC – 2018-06-24T18:52:50.640