"In here" is the place where you are or that you have shown that is enclosed by walls or some kind of borders, usually a room of a building, but it can also be a zone, like of a map. "Where is the puppy? He's in here, in the house."

"Over here" is the place where you are or where you have shown, and it emphasizes that some movement is needed to get to this place. "Pass me the ball! Over here!"

"Right here" is the place where you are or where you have shown by context that emphasizes this place instead of another place. "Where are my keys? Are they over there? No, they're right here!"