Each item in the list represents an individual trigger. You can add or remove them by using the + and - buttons on the bottom of the pane. The columns are as follows:

1. You may use the checkbox to turn a trigger on or off
2. Under the Command column is a description of the command
3. The Type column has an image indicating what type of trigger it is
4. Finally, the Trigger column has a description of the trigger required to activate the command, be it a keystroke, mouse event, etc.

Some triggers (such as mouse triggers) require use of the inspector drawer to set its properties. To access the drawer click the i button in the bottom-right corner of the pane.