"Still, I don't understand what it means to add the folder to the path"
Like many programming languages MATLAB has a path which is an explicit list of folder where it will look for code. It would not be efficient, useful, or probably even feasible for a program to look "everywhere" for code, thus an explicit list of folders is stored. This is called the "MATLAB path" or the "search path":
The current folder is implicitly always first on the MATLAB path, so the current folder will be searched first for code.
To use functions like dir simply define an absolute or relative path, following your OS and drives:
Rather than changing folders (which is slow and makes debugging harder) you should practice using absolute and relative paths (e.g. keep your data and code separately, and write your functions to accept the path of where the data is stored).
