Using a conditional logic in your form
In your form, click Advanced > Logic in the top navigation bar (under the the form title).
Click Add Logic.
You will be taken to the logic designer, where you can build your logic.
Give your logic a name, so you can find it again later.
Choose Conditional as the type.
Build out your logic (see subsequent pages in this section)
Click Save. You can now use this logic in your form.