No reason to be! They’re just another human being trying to do their best for your company and team. Assume best intentions!
If you’re nervous because you have no idea what to say to broach the topic, here’s something you could try.
“Hi, I’m Charlie. I work for Susan over on the infrastructure team. As part of my own professional development, I’m trying to build out an understanding of how all of the people at our company move towards our common goal, as it’s not always obvious to me at my level. Do you have time for a quick one on one where you can share with me your roles and responsibilities, and what some of your challenges are here at our company?”
Basically, you don’t need to say something as blunt as “What exactly is it that you do here?” Instead, just come at it from a position of positive inquiry where you’re just genuinely trying to learn and grow.
I say all this because no answer here is going to really tell you what that person does. Everyone’s roles and responsibilities vary, regardless of their title. You won’t learn unless you learn how to ask!