[AccessD] Process multi-select listbox

I can't remember how to do this. (Been concentrating on SQL for the past while.) I have a multi-select listbox whose column of interest is a single-letter such as "A", "B", "C", etc. I want to grab all the selected items and create a string by concatenating the single letters.

Something about lstMyBox.Selected with a For/Next wrapped around it, but I'm fuzzy on the details. I've done it in past apps but cannot remember. 

Pushes in the right direction appreciated.
TIA,
 
Arthur