Importing allows you to bring your existing items onto Vendoo from one of the marketplaces, so that you can easily crosspost them to the other sites.
The Delist/Relist feature is a way to remove a listing from a marketplace and then post it as a new listing. In addition to refreshing old inventory, this feature also allows you to automatically delist your sold items.
The 4th Marketplace allows you to list your item on all four sites.