The first step in the Walmart setup is to link the integration, and otherwise connect as normal.
The initial push of listings to Walmart will take approximately 30-60 minutes. You can check the status of the push in the Walmart Seller Portal at https://seller.walmart.com
After you have successfully pushed at least 1 SKU, you need to contact your Walmart account rep. They will send 2 test orders for one of the items you submitted. You need to approve one of these orders, and mark it shipped with a real but expired tracking number. The other order you need to cancel.
After you do this, your Walmart account rep will approve your account, and you can go live. This will make all listings pushed from Listing Mirror to Walmart show up on Walmart.com. The normal lag time for new listings is approximately 30-60 minutes.