About "here"

Could anyone please explain the usuage of "here"?
for example:
Is anybody here?
Is anybody in here?
What's the difference? thanks!

I'm not sure about that, Suzi. Outside a room, just before opening the door to have a look, I might say "Is anybody in there?", But not "here" - "here" is too immediate. It can only really mean "at the location of the speaker".

The only difference I can think of is that "in here" defines the boundaries of "here" more precisely. It suggests that you are enclosed (in a room, for example), and you are asking if anybody else is in that room. On the other hand, "Is there anybody here" (without the "in") could be used outdoors - or it could be used indoors when when the "here" in question isn't just one room. For example, a coach at a sports club might ask "Is anybody here yet?", meaning "Has anyone arrived (in the building, not necessarily in the room) yet?"

There's very little in it though. "Here" is where you (the speaker) are. Whether or not you can use "in" (or "on", or "under", or any other preposition in fact) is really only a matter of whether or not it makes sense to do that, and whether or not there would be any point.

Rommie