The end user will see the Power Actions™ in a toolbar on the issue view.
The custom field shown above, actually defines 3 actions, but each has a different condition; Action 1 is enabled, Action 2 is disabled and Action 3 is hidden and thus - not visible on the UI.
You can easily spot Actions that require a screen by the trailing "..." in the labels.
To execute an action, just click the respective button. If the action requires an additional input from the user, a dialog similar to the one below will be shown before the Action Script will be executed.