Payment Full - Fully payed commission in front, your commission shall be discussed personally, made and sent to you.
50-50 - functions the same as Payment in Full, but you part half the total value before work starts. You can only receive the files after the other half is paid though.
Payment Plan up to 4x - you can have a commission slot by a quarter of the price, but work only starts at the second pay and you may only receive the files once payment is complete. You should receive an invoice each month on your email warning you about the upcoming payments.

Each of them works by letting me know of how you want to pay for your commission. You shall receive an invoice with the determined price and once paid accordingly, work starts. In all cases, you only get the complete file package after the payment is complete.