Supplier Name - start tying in the field and it will automatically search the contact in the database. If the contact is not available, it will prompt you to add the contact by clicking at the name.
Date - by default it will have the today's date. You can always change it to another date.
Payment Method - it has 4 options; EFT, Cheque, Cash and Credit Card
Reference - anything to remind you about this transaction
Items - you can either Add New Item here or select from the Items you added previously
Description - description of the item you are paying for
Quantity - quantity of the items you are paying for
Discount - discount is in percentage
Price / Unit - price per unit of the item you purchase
Account - select account appropriate for the purchase
Tax Rate - select tax rate appropriate for the purchase (if any)