Linux Path Basics
Paths are one of the most fundamental concepts in Linux -- and one of the easiest to get stuck on at the beginning. Relative paths, absolute paths, current directory, home directory, system directory: if you don't sort these out first, you'll quickly run into "I typed it correctly, why can't the file be found?" situations when writing commands later.
This material works best when paired with an actual terminal: every time you see a path concept, run pwd, ls, and cd on your own machine -- much more effective than just flipping through slides.