A required element must be filled out by the user before the form can be submitted.

Making an element required

Single Line Text → Settings

Tick the box at the Required field to make it required.

Required error message

Single Line Text → Settings → Optional

Change the required error message by entering text into the Error message if required field.

Required indicator text

Settings → Style → Labels

Change the text indicating the element is required. By default this is (required), but you may want to make it an asterisk * for example.

Still having trouble? Head over to the forums.