Using Pebble
Pebble has four buttons. The left button is called the 'back' button, which is used for returning to the previous screen or entering your watchface app from the main menu. On the right side, the top and bottom ('up' and 'down') buttons generally are used for scrolling through lists. The center button is used to 'select' an item in a list or start an app on Pebble. It can also be used to get to the main menu from a watchface.
Though most navigation is done with a quick press of a button, some apps incorporate longer presses to expose more options, as seen with he music volume control below.