Hi there is often used when the speaker does not know the person's name ... so you might say "Hi there" to a child you see that sits next to you on the bus, and you would say "Hi" or "Hi Mom" to your mother.

generally speaking it is means hello

Hi "there" kind of means like, Hello to you over there. Like psmithphil said, it's basically to acknowledge your existence, and show you notice the person in a way.

"Hi there" is just a way many people say "Hi". I suppose when I say it here in the USA I'm just showing you exist. Silly I know but don't be concerned with it. You only have to realize they are just saying "Hi" or "Hello" and ignore the "there".