By default, the HUD has 5 slots, to which you can add your favorite EEP settings. To activate an EEP setting, simply click the respective button.
Add EEP settings either by name (for built-in viewer settings), by UUID for settings that you have in the "Settings" folder of your inventory, or you can record the currently active settings.
The package comes with a kit so you could assemble your own HUD with as few or many buttons as you like.