how do you use the pen witin powerpoint, not in the slide show format?

Hi Rachel, Thank you for the question, welcome to the forum, In answer to your question;
I am not aware of any way that the pen can be used other than in Slide Show view, as you have discovered PowerPoint offers a little known pen tool, which can be used to write over existing PowerPoint slides or on a blank (black/white) screen. By choosing a contrasting color you can suspend the mouse functions and use the pen to draw and write on the screen.
This allows for spontaneity, e.g., "What happens if this item was moved here? or perhaps underlining a particular point" These annotations are not preserved as you change slides: a single, possibly premature, key press and they vanish. Nevertheless, having a pen tablet as you present your PowerPoint is a vast improvement on PowerPoint alone and allows for interactive presentations. To choose the pen and arrow pointer options, look for the nearly invisible icon in the lower left corner of the screen during a PowerPoint show, or right click and choose the option Pen Options. I hope that has helped, if so please click the Resolved link, best regards Pete