Sending an email to the respondent upon form submission is a very common need, luckily it's very easy to set up.
Before we begin: You must have an "Email" question in your form before you can set this up.
In the form editor, go to After Submission → Emails and press the "Add Email +" button.
In the "To" field, choose the email question from the form that you expect the respondent to put their email address in.
Fill out the rest of the email setup to specify what the contents of the email should be (e.g. subject line, attachments, and messaging).
When you're ready, click "Add Email".
Save and view your form, then run a test submission with your email address to receive the email.