What might you do in a typical first session with a student?

I would go over what the student has learned in this area so far, and what s/he is hoping to get out of tutoring. Before starting tutoring, I find that it's important to establish goals, so we can check our progress along the way.

What techniques would you use to be sure that a student understands the material?

Techniques can vary depending on what type of learner the student is: visual, auditory, kinesthetic, or something else completely. Normally I try to explain examples from the material, then ask the student to go through the material and try to explain how they would tackle the problems or material him/herself. This technique is a combination of all three kinds of learning.

What types of materials do you typically use during a tutoring session?

The materials I use depend on the subject, and what the student brings to the table (literally). I have suggested books, apps, and websites for language learning and GRE studies, but it's up to the student whether or not s/he wants to add resources onto his or her own materials.