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.

Action Shortcut
Put a window into floating mode MOD + SHIFT + SPACE
Open Dmenu MOD + D
Close a tile MOD + SHIFT + Q
Switch between workspaces MOD + Number (1, 2, 3, etc.)
Open a terminal MOD + ENTER
Quickly restart i3wm MOD + SHIFT + R
Put focused application on another workspace MOD + SHIFT + NUMBER (1, 2, 3, etc.)
End i3 / X session (log out) MOD + SHIFT + E