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
:
When the bar reaches the bottom of the screen, the list scrolls up to show the remaining options. Having selected the one you want
...
press the 
key to enter it. You can also use the application shortcut, listed to the right of the name. Here's the complete list of available application shortcuts:
Diary
D
PipeDream
P
BBC BASIC
B
Calculator
R
Calendar
C
Clock
T
Alarm
A
Filer
F
FlashStore
J
PrinterEd
E
Panel
S
Terminal
V
Imp-Export
X
...
L
...
Creating a new activity
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: