After you have completed the project work, you have to notify the project customer via e-mail or using the Project Message Board. You can do this after or before you hand over your work to the customer.
Up to the moment, the amount of money for the project is safely stored in the project escrow account. This way you can be sure that you will be paid for the project even after you handed your work over to the provider.
The customer reviews the results and completes the project. The money is immediately transferred from the escrow account to your account in ProjectLab system. You can check if you received the payment in "My Account" section of My Office. You can withdraw it at any time. More info on Managing your Money Account.