Sony VAIO VAIO PCG505F User Manual page 34

The plastic pen, located in the vinyl bag with your User Guide, can be used
on the touchpad for drawing or for signing your name with the
ScribblePad software. You can store the pen in the pen compartment on
the left side of the LCD screen.
Press the bottom of the pen compartment to open the compartment.
Slide the pen in or out of the compartment to store or remove it.
When you are ready to close the pen compartment, press the top of
the compartment until it clicks into place.