Payment information is automatically collected from your Marketplace Channels; however, if you accept Cash, Money Orders, or other non digital forms of payment (not recommended), or if someone pays you from a different PayPal account then you may need to enter the payment manually.

Start by clicking the Edit icon next to the Draft Order that you wish to add the payment to.

Scroll to the bottom of the order and click the payments tab.

Simply input the information and click one of the Save buttons.  The amount due will be recalculated upon save and the order should display the correct payment icon in the list.