Adding or editing category names in a budget

Pull down the Window menu to Categories. Click the + icon to add a new main Category. To add a subcategory, click on the main category first, then click the + icon. To edit the names of an existing Category, click on it and then click the pencil icon to edit. (Note that you can't edit any Categories with a Status* of "Required"; Quicken will reject an editing change or attempt to delete one.)

*If you don't see the Status column, Control-click on any of the column headings. There will be a small opt-up menu where you can check any (I'd suggest all!) the columns to make them visible.