In MS Word, some files look different “on the page” in the computer. What causes this?

It’s called page view. Yes, you can set your program to show you the pages in different ways. It’s easy once you know how. Look down the screen to near the start button – where there are several “lines” of gray “stuff” before you see the bottom edge of the document. At the top left of all of this gray are 4 buttons before the side-to-side scroll bar starts. The page view with the dotted line to show page break is called “normal” and it is that far left button (depressed) – the arrow below is pointing to these buttons:

To see how the other 3 views work, position a file where you can see the page break and just left click each button in turn. Besides normal view, I sometimes like print view which is the third button from the left, as it shows me virtual sheets of paper with the correct margins and page number too. – CAC