Go to zapier.com and create an account. (Free for 100 actions/month)
Log in to your Zapier account
Search for Groundwork from the Zapier dashboard
Navigate to the Groundwork dashboard
Select the "Setup" tab
Select the "Integration" tab
Copy your API key
Zapier will ask for your API key when setting up new zaps. Be careful not to click generate new once you have existing zaps. Doing so will break your existing zaps.