Account, Name and Phone are used as "look up" fields from the POS. Don't change them more than necessary.
For delivery customers the Memo Fields show up on the Delivery Screen and the printed receipt, and can contain special directions for the delivery driver.
For House Accounts the balance and limit fields are used to set and monitor limits for the account.
Other fields are customized by client, and may have different labels and descriptions based on a particular use. Check with your support staff to verify the usage of individual fields.