The CAPTCHA field is the Javascript tool that scans a browser and may force people to complete a visual or audio challenge in order to submit.  Every site should currently be set up for CAPTCHA usage for all users who have access to Gravity Forms.

To add a CAPTCHA field to your form, open your form on the backend, and look for the ADVANCED FIELDS option on the right. Once selected, you will see a bunch of new options appear, including "CAPTCHA". Select this option and the new CAPTCHA field will appear at the bottom of your form. You can drag and drop it to anywhere you want in the form, but users expect it at the very bottom, so we recommend that you leave it there.