Navigating i3wm can be difficult coming from a regular DE. Here are some basic shortcuts to use, which can make your life easier as a beginner.

Almost all of these shortcuts use the "mod" -key, which is configured to be ALT or SUPER by default.

Putting a window into floating-mode: MOD + SHIFT + SPACE

Dmenu is the place where you can launch applications.

Open Dmenu: MOD + D

Closing a tile: MOD + SHIFT + Q

Switching between workspaces: MOD + Number (1, 2, 3, etc.)

Opening a terminal: MOD + ENTER

Quickly restart i3wm: MOD + SHIFT + R

Putting focused application to another workspace: MOD + SHIFT + NUMBER (1, 2, 3, etc.)

End i3 / X session (log out): MOD + SHIFT + E