Go to Agreemint Sign Up page and create an account. You will need a valid email address to receive your confirmation code.
Once you have logged in, find the "Clickwrap" menu option on the left and select "Settings":
On the settings page, click the "Create API Key" button
This API key will be associated with this account. This key should be kept PRIVATE, as it allows access to all clickwrap documents associated with this account. If you believe your key has been compromised, or regularly replace keys, you can use the "Delete Key" button to remove the current key and then create a new one.
The API can be used in conjungtion with or as a replacement for the Agreemint Clickwrap UI.