The HTML on the left is interactive, you can change the elements are included and the
form to the right will be updated immediately. You can press the blue Submit button on
the right to see what data gets sent.
Copy the checkbox example HTML around line 168 above the blue Submit button around line 82 to try it.
If you already have a trial FormKeep account you can replace
with your form url
from the Setup page and you can see the data get saved and get email notifications as well.