To install a new module on Prestashop:

Enter the back office and select Modules> modules from the menu
Click the “Add new module” button
Choose the file to upload and click the “Upload form” button. Check that the version of the module is updated, for security, upload the file twice so as to get around a problem of some old versions of Prestashop in updating the modules.
Install the module from your Prestashop panel, searching for the “Fastbay” module in the Market Place category.
Prestashop 1.6

IMPORTANT Once installed, make sure that all files and folders of the eBay module have write permissions (typically 755 or 777 for folders, 644 for files depending on your server)
If you get errors from your server (for example the size of the uploaded file exceeds the allowed limit), you can upload the form manually via FTP:

Unzip the .zip file you downloaded.
Enter the store root on your ftp server: you will find the “modules” folder there.
Drag the new form into the folder. Activate the new module in the back-office, “Modules” menu.