There are 2 types of additional fields you can add to your contest.
Signup fields are added to the contest signup in addition to the name / email fields. They look like this. (Note where it says "what industry is your business in?")
Please note that you can only add 3 additional entries.
Custom entries, on the other hand, are asked AFTER the signup. These reward extra entries to your contestant.
They are set-up in the social / entries tab.
Then click the button for "Access custom entries"
You'll be able to set-up and edit your custom entries on this page!