Your first meeting with your new employee should be introductory in nature. Tell them about yourself and how you came to work at HSPH, show them around your department, introduce them to their colleagues, and direct them to where they will be working.
Explain to the new employee how they can contact you during the day, and make it clear that you are available to them as when required, but that they should use their discretion at all times. Explain that you will be meeting regularly (see below), and that non-urgent issues should be left until those times, but that anything that is materially hindering their work or performance can be discussed with you immediately.
Ask if they have any initial queries or issues, and deal with them. Then leave the new employee to get on with their assignment! – remember, your role is to help the new employee get on with the task at hand, not to prevent them from doing so!