If you type HELP in the console, you get a list of commands...

just now I noticed the "ADD" command. It says "to add files".

What does that mean? Can I add external text or image files? Or maybe point to other .tic carts in the same directory? What's it used for?

Okay, I found that it copies the file I pick to the current tic-80 directory... But why? 

With the ADD command you can copy any file to internal file system

On some platforms you can't open TIC directory (like HTML version), so you can use ADD then

Okay...I gotcha. thanks