These are all prepositions. They show the relative location of one object to another. If you want them used specifically with the word 'here,' here is the following: "I'm writing on here." (paper) "It's getting hot in here." (inside a room) "Don't put your junk over here. Keep your junk over there." Over kind of represent one spot of ground versus another spot on the ground. Do you have a specific example of a sentence that confused you?

"____ is over here." This basically means "____ is here", but the 'over' emphasises that the person you're speaking ISN'T here. "____ is in here". This means that the subject is in something. You should be pointing at whatever it's in when you say this. "____ is on here." I'm struggling to think when you'd use this... the only time I can think of this being used (when 'on' is a preposition) is when the subject is attached to or on top of something (ie. 'on' it). For example a poster attached to a wall or a person standing on a roof. 'On' can also be an adjective used to describe that a program are running. For example, "The play is on (here)".

http://www.italki.com/question/200624