"I can't leave here."

Teachers, in the above sentence I thought the verb "leave" is supposed to be followed by nouns. But in the above sentence, "here" is clearly an adverb. I've seen this sentence (leave here or there) a lot, though.

So please anyboy tell me why "here" is used after "leave" and it's okay.
It's okay. You don't have to have a noun after leave. here is almost redundant. If you just say I can't leave, it means I can't leave (from) [ here / this place] .

I can't leave now is another example where leave is not followed by a noun. It means I can't leave this place now.
Just a little grammatial explanation that you can ignore. "Leave" in its "go away" meaning can be used both as transitive (in which it needs an object or noun) and intransitive verb (your example, or CJ's : I can't leave). In other senses, you'll need an object, or sometimes two, to follow the verb. I hope that I haven't confused you.