The first thing you have to do is create the field in your company profile.
Go to My Links -> Company -> Profile -> The Lot Attributes tab
Find the field "Company 1"
In the first box enter the field name. If you want a default put it in the second box. Then put all of your options into the last field separated by commas (See Picture for example).
Then for any auction you can turn it on by going to Auction -> Edit Settings.
Finally see your field in action on the Lot Builder/ Lot by Photo pages.