When Float first imports data from your accounting platform all chart of account categories with value are automatically added into the cash flow table.
On the flip side, any that are 'empty' (don't yet have value) aren't added in and are instead stored in the Category Manager. These 'empty' categories can easily be added in by using the 'Add category' option shown in the Category Manager.
Clicking this option will generate the following modal with the options for adding a new category.
Select the category you want to add, the type (cash in or cash out) and if it should be a part of a group. If you haven't set up any groups, you can check out how to here. Once added the category can be budgeted against in the same way as any other category.
Note: If an 'empty' category hasn't yet been added to the cash flow and value is assigned to it in the accounting platform then the category will automatically be added and the value will be displayed in the cash flow.