If you have an invoice for an expense that should be applied to various categories, then that can be achieved by clicking the "Split?" option on the expense after you've selected the vendor. This is very typical for Mortgage payments. A Mortgage payment usually has Interest, Principal and escrows such as taxes. Once the split option is checked, you will notice a section where you can add additional categories and the amount per category. Memo is an optional field, but you may use it if required. The total amount of the invoice will be automatically calculated based on the individual line items.
Once you complete and add the categories, be sure to click Add to add the expense.