After you order a service, your purchase page will have a link to your new project page. On the project page, you'll upload a reference mix, a zip file of your session and audio files. You'll also tell the seller the details of what you want.
In the buying dashboard on the sidebar menu, click services and select the service category you want.
On the category page, click the service you want.
The displayed sellers provide your service. Use the speaker button next to the service to hear their audio sample of that work. Use the pricing button to display that seller's order form.
Fill out the seller's order form to see the price. Click add to cart and checkout to buy the service.