By selecting the "New" button, the "New Category" menu option of the "N" command shortcut, you will see a popup asking for the name of the category and the portion of the unallocated budget to be made available to the category. Select "OK" to confirm and add to the list or "Cancel" to ignore the information.
Selecting "Done" will then return you to the main account list screen.
You will have the option of selecting to carry over any un-spent amounts to the next month if you like. By default, you will reset the totals of all accounts. If you select "Reset only marked" then only those accounts marked with a ® symbol in the Account List will be reset. Select "OK" to action the reset or "Cancel" to return to the Account List without resetting.