Hi Doni!
Company galleries are built with keywords. So you would choose your member gallery and then in the keyword field include the company keyword with your other keywords. I have a video in my signature that explains how other galleries are built which you can watch when you have just a minute.
But to find what keywords companies use, just go to this page:
My Favorite Things, Scor-Pal, Stamping Bella, Sweet 'n Sassy Stamps, Taylored Expressions, The Cat's Pajamas, The Greeting Farm, Unity Stamp Company, Verve Stamps, Your Next Stamp - Splitcoaststampers Member Company Galleries
Where you see the list of Galleries by Company, hover with your cursor over any companies you see in the list. Their keywords will be displayed at the bottom left of your browser.
Or, if you click one of those links and go to their gallery, at the top left of the gallery, you'll see: Home > Search: KEYWORD(S) for that company