Open will automatically detect and categorize all transactions that have been created via Collect and Pay, based on category you have provided while created collections and payments. If you haven’t chosen any category, some of these may remain un-categorized. You can edit most of them via Transactions tab or while creating invoices/ bills/ fund transfers.
Make sure to select the relevant categories so that they would not need manual categorization at a later point. This will help you in getting proper accounting reports and know where your business is heading