Quick video that walks through the instructions below
Instructions
Login to your Teamtailor Account
Click on your Company Name in the top-right and then click Settings
Click on the API Keys link
Click the New API Key button
Name the key and set the API Scope to Admin
Check both the Read and Write checkboxes
Click the Create button
Copy the API key to your clipboard
Enter your API key into the API key box on Hired, and click Connect