Step 1: Head over to https://apps.shopify.com/onecart
Click on 'Add App'

Step 2:  Log into your Shopify account

Step 3: Install App

Step 4: Login to your OneCart account

Step 5: Shopify store connected

Once you have successfully, login to your OneCart account, you will see a green banner at the top. 

You're done! Your Shopify account is now connected to OneCart! :)