I just started working with Movable Type, and in particular MT 5 (OS) . Can someone provide a simple overview on how to add Custom Fields for an Entry? Say for instance I wanted to add a Field to each entry for "Company", do I do this in the theme.yaml file somewhere?
Reported on Movable Type 5

Welcome to MT.
http://www.movabletype.org/documentation/professional/custom-fields/
should have the answers you're looking for.
-tony
Thanks for that Tony. I saw that in the documentation, but I am using the Open Source version, not Pro. Is it possible to add Custom Fields in the Open Source version? I downloaded the Open Source version assuming it was more customizable than the Professional Version ... but maybe I should just be using the Professional Version?
I'm wondering the same thing as you, gregoryttp. Hopefully, we can figure this out. Have you found out anything yet?
The custom fields feature is one of the things that set the Open Source and the Professional version apart. So if you want to use custom fields, you need to be using the Professional version...