Respondent questions should be added to the survey in order to capture the respondent data. For your ease some fields such as Full Name, First Name, Last Name, Email, etc. are pre-provided. You can also add more fields as per your needs.
You can also track the repeat respondents for your survey by capturing certain respondent fields. Name, Email, and Phone number are the fields that are used to track the repeat respondents, so add these Respondent Questions in order to evaluate your repeat respondents data after enabling Respondent Tracking from the Settings.