If I have a cell that is multiple lines of text, I can drag the top bar down to see all the different lines in the cell, but when I hit enter, the cursor goes out of the cell and onto the next.
How do I move up and down the text within a multi-line set of text within one Excel cell?
Just press F2 on the cell. That will put you in edit mode in which it is possible to use the arrow keys. If you want to enter newlines in the cell yourself, you have to do that with alt + enter.