Local and national laws apply to employment and recruitment interviews. The laws prescribe what is allowed in an interview, and it is essential you understand what is and isn't legal.
For example, if you are interviewing several people in a day, it is often difficult to remember who said what. If you write "ginger hair" as a reminder on your paperwork, you are opening the door to a claim for discrimination.
Selecting someone through an interview is a form of discrimination. The reasons for your selection must be legitimate in every applicable case.
This isn't a reason to be over cautious. As I said earlier, preparation is the solid foundation which makes the manager, you, appear in control. Experienced managers have done this several times so will have the foundation. As a new manager, you can prepare and practice thoroughly and catch up on the experienced managers.
The anti-discrimination principles are simple enough even if the practice can be fuzzy around the edges. As a result, it's probably best if you simply avoid the edges.
Anti-discrimination laws vary from place to place, so you need to check the laws where you are. However, the basic principle is that you can discriminate for reasons relating to a candidate's ability to perform a task. You will measure this by asking questions and gauging the responses. What you must not do is assume a person's ability based on an observation or answer to a question about their life. You must not assume that just because I am 63 and overweight I don't have the ability to do a strenuous manual task. You must ask questions about my skill and performance of those tasks instead. To reveal my capability, ask about performance, not characteristics assumed to be linked to performance.
Search the Internet for "employment discrimination" to find more guidance about discrimination laws which apply to your location. Example sites are as follows:
Cornell University Law School Legal Information Institute: http://www.law.cornell.edu/wex/employment_discrimination.
U.S. Equal Employment Opportunity Commission: http://www.eeoc.gov/.
UK Chartered Institute of Personnel and Development: http://www.cipd.co.uk/hr-resources/employment-law-faqs/discrimination.aspx.
UK Government website—working, jobs and pensions section: https://www.gov.uk/browse/working.
To calm the candidate, you need to appear calm yourself. I spoke earlier about your performance being important. Remember, to the candidate, you are the organization, so you need to prepare yourself. The next section will help you do that.