Adding and editing categories
Go to Admin → Setup → Categories (if the program only has one category, this menu item is labelled "Entry Form" instead and opens that category directly). Click "+ New Category" to add one, or click a category's name to edit it.
On the category edit page you can set: name, short name, description, entry cost (ex-GST and GST split automatically from your tax rate), category type, and the flags that control its lifecycle: Entries Open, Judging Open, Score Ready, Winner Nomination, plus "admin only" (hidden from the public entry list) and "exclude from auto open/close" (skip the Automatic Actions scheduler).
Each category has its own Questions, Eligibility Rules and Judging Criteria assignments, edited further down the same page. Click "Preview Form" at any time to see exactly what an entrant will see when entering that category (eligibility questions, entry-form fields and judging criteria) without needing to submit a real entry.
From the Categories list you can also reorder categories (drag the order numbers and click Reorder), inline-edit the cost, copy a category (duplicates its questions/eligibility/criteria to customise), or delete one.