You have created your market and now you want to invite vendors to join your market. Its very easy. Just tell your vendors to follow these steps.

Step 1 : Vendor would download Nearby Shops from Google Play

Step 2 : Vendor would Select the Given Market

Step 3 : Vendor would Login to the app

Step 4 : Vendor would click "Become a Seller" option on Market Screen / Profile Screen

Step 5 : Vendor would fill Shop information and Click on Add Button

Step 6 : Market admin would Enable the Shop from his Admin Dashboard

As a market admin unless you dont approve / enable a shop it wont be visible to the customers. This is done to ensure that market admins can enforce rules and regulations.

After all of these steps are complete the vendor would also need to setup his shop and make it ready to receive orders. The instructions to setup your shop is given in another tutorial.