Keyboard shortcuts are set by clicking on the Change button for the appropriate shortcut, and then typing the keys you want for that shortcut. If the keys are not valid, they will not appear in the text field. Beware of using common keys, like letters or numbers without appropriate modifiers.
What each shortcut does should be self explanatory:
Popup Menu
Close Window
Close All Windows
Next Tab
Previous Tab
Rename Tab
Detach Tab
Close Tab
Preferences