If your template doesn't already feature an email address field, you can select the Email address element from the 'Build' side panel and drag it in. Click on Type question here to then enter your text for it.
This element is already prepared to accept an email address, therefore email validation is automatically configured (but you do have the choice to write your own validation error message).
If you're assigning questions to contact data fields throughout your survey or form, then you'll need to have this element assigned to your email address contact data field to ensure you're successfully collecting and assigning all the data you require to your address books. You can find out more about this in Assigning questions to your contact data fields.