When you create a dropdown field all the values that appear in the list are actually in a different table. When you are in the invoice screen, for example, the Customer dropdown shows you all the customers from the Customer table.
So in your case you created a new dropdown field, I'm guessing, in the Customer table, called say "Widgets". Therefore, Method created a Widgets table to store all the possible selections.
So what you need to do is just modify the contents of the new Widget table. If you go to Customize > Screens, you'll see that we probably already created a screen for you. Just find it and click the View icon. You can modify this Widget table to have other fields, like "IsActive", and "Description" that bring more meaning to your dropdown - and then you can modify your Widgets screen so that you can show your fields and provide extra functionality.
(Obviously substitute Widget for the real name of your field and table!)
In terms of putting them on the invoice, you can customize the invoice print out using the Method Report Designer, which you can access by clicking More Actions.. > Customize Print Templates... from the invoice screen.
Which table do you add the field to, the Customer table or the Invoice table?
Paul