Make sure you are logged in; if yes,

Step 1: Click on the Apps from the navigation bar.

Step 2: Select the Braintree from the given apps.

Step 3: Click on the button "Add Account+"

Step 4: Fill in the Public Key, Private Key and Merchant ID given by the Braintree account.

Step 5: Click in the button Connect Braintree.

Step 6: That's it. Your Braintree account is now connected with FF Inventory. You will see a message window like below on a successful connection.