Categories is an overview all of your business categories and their balances. This is can be useful to see if your balances appear incorrect and need be analysed.
New categories can be added if required and unused categories can be deleted (or hidden if they have been previously used but no longer have a balance). There is also the option to see all categories, not just those with balances.
From Categories you are also able to enter adjustments. Adjustments are used to transfer amounts between categories.
You may never need to use this feature as adjustments are used more at your year-end for things like depreciation of assets. Your accountant should either enter the adjustments for you or give you the information to enter them yourself. If you are unsure about entering an adjustment always consult your accountant first.
To learn more about Adjustments click here.