When you've been selected as a winner in a design project, you and the client will have a private wrap-up area where you'll complete the project.
After you and the client sign the project contract, you'll have an opportunity to send proofs to the client. Do not provide final, high-resolution files. At this stage, you want to be sure that the client doesn't have any more tweaks to the designs and once the client approves your proofs, you can create all the necessary final files.
Upload your proof in a PDF, JPG or PNG format so that the client can easily review the proof.
The most successful creatives have a formal proof sheet they'll use at this stage. For example, here are the standard proof sheets we recommend for logo design projects.