To avoid getting a lot of spam submissions it is important to add a Captcha challenge. First click the "View" tab to view your form.
Then click the "Captcha" link and click "Place CAPTCHA here for untrusted users."
Note that this shows up on a lot of different places, but this is the only place you do this to get the Captcha on your form.
After clicking this you will get this next screen.
There are options for several types of Captcha, but we only want to use reCaptcha. Select this from the menu and then click Save.
You form is now protected from spam submissions. Note that logged in users will not see the Captcha, only anonymous users.