Modes are the whole game
Here is the one idea that makes Zellij make sense. Zellij is modal. At any moment you're in a mode, and the mode decides what your keys do. You spend most of your time in Normal mode, where keys go straight to your shell. To do something to the workspace, you switch into a mode built for that job, act, and drop back to Normal.
Each mode is entered with a Ctrl chord from Normal, and the same chord (or Enter, or Esc) drops you back out. The chords spell themselves: pane, tab, scroll, and so on. Learn the entry chords and you've learned the map.
Two chords are worth burning in early because they work from almost everywhere. Ctrl g locks the interface, and Ctrl q quits Zellij entirely. Don't reach for Ctrl q by reflex; it tears the whole session down.
Try it yourself
Take the mode tour
Feel the modal model in your hands. You're not doing anything to your workspace yet, just entering and leaving modes and watching the status bar change.
Tick every step to confirm you did it.
Same key, different mode
You press Ctrl p, then n. What did n just do?
Getting unstuck
The most important reflex in the whole tool.
You're in some mode and you've forgotten which. What single key reliably gets you back to Normal?