You can create a showcase from the Dashboard, or from the Showcase link accessible from your Dashboard.
After clicking the Create a showcase button you will be prompted to enter the showcase name.
After naming your showcase - if you own collectibles - you will be prompted to add collections to your showcase. Rather than adding individual collectibles to your showcase you add entire collections. . This includes all the collectibles in the collection, not just those you own. This means you may see collections that you did not create
You will be able to filter showcases to see only the collectibles you own and you will be able to add individual collectibles from your showcase to the public market place.
Now that you've created your Showcase you can Add Collectibles to the Cargo Marketplace.