Folder structure file names

I know this is a basic question (I have a lot of these) but I’m a bit confused how to handle folder structure in my file linkages.

For example if I make a page in a subfolder I’ve noticed that I have to change my file in include properties to …/includes/Include.php when it is normally /Includes/Include.php

This method worked fine until I needed to make a data page in a subfolder. I couldn’t get it to work so I tokk a working page and did a “save as” into the subfolder and it quit working. The changes above fix the includes but I don’t know how to get the data working??