When you run a MatLab file, your current folder (often displayed on the left hand side) must be the one where that file is stored.
If you try to run that file from a different folder, than the dialogue box come up and it gives you the following choices:
Change Folder: changes the current folder to the one where the file is stored, so that it can run it.
Add to Path: adds the folder where the file is stored to the top of the search path for the current session, so that it can run it.
