This should be fairly easy, but I'm getting a headache from trying to figure it out. I want to list all the coordinates between two points. Like so:

1: (1,1)
2: (1,3)
In between: (1,2)

Or

1: (1,1)
2: (5,1)
In between: (2,1), (3,1), (4,1)

It does not need to work with diagonals.

You appear to be a beginning programmer. A general technique I find useful is to do the job yourself, on paper, then look at how you did it and translate that to a program. If you can't see how, break it down into simpler steps until you can.