To enter an application, or a popdown, you simply have to select its name on the APPLICATIONS menu by moving the highlighting bar up and down with the cursor keys and :
Entering PipeDream or BBC BASIC from the Index APPLICATIONS list creates a new, blank document.
For example, to enter PipeDream, starting with a new blank document, move the highlighting bar until PipeDream is selected, and press the key; you will then see the PipeDream screen: