There are keyboard shortcuts for most major functions. To see a list of them, go to View -> Keyboard Shortcuts in the hamburger menu at the top left of the screen (Windows/Linux), or the app menu (macOS).
Shortcuts for some features such as Zen Mode only work when the focus is anywhere on the app UI except the active webpage.
In case a feature does not activate with a shortcut, try clicking somewhere outside the webpage, then use the shortcut again.
This will open a list of shortcuts that you can scroll through.
Alternatively, you can access the same dialog box by clicking on the ⚙ Settings icon on the top right of the screen, and navigating to the Shortcuts section.