Help with Creating a FUNCTION

I’m creating a menu using MC for each menu item. Each menu item MC consits of two frames. One for when the selection isn’t clicked on, and one for when the selection has been clicked. Basically, I figure I need to write a function to decide what button has been clicked on and also which one was the last that was clicked on so I know which one to send back to it’s first frame (I know it sounds confusing).

I could really use the help with writing a function. I checked out the tutorial, but it didn’t seem to explain what type I should use and how to code it.
All I want is when you click on a text button that it goes to BOLD and the last button that was clicked on goes from BOLD to normal.