In this page, there are three options for transfer
Full and final payment for completed project: Choose this option if you are satisfied with freelancer's work.
Partial payment for project: In some cases, freelancers might require initial payment before beginning the work.
Other reason: For any other reasons, you may use this method
When you choose the first or second option, the shows list of completed projects. When you click on a project, it automatically fills the Username to which the payment has to be done and the Amount to be sent. When you click on Transfer, the details will be saved and will not be sent to the freelancer. This is just security measure before it is sent.
You need to go to Manage Payments → Outgoing Escrow Payments and Release the payment.