(They have a super-cool alien-technology-enabled translating device, so they understand English.)
They've asked you to tell them about the room you're writing them from.
Try describing a few things around you, but remember that they have no knowledge of human culture.
How would you describe a mechanical pencil to someone who doesn't know what writing is, what paper is, or what human hands are?
How might you explain a painting of a beach landscape, when they won't know what paint is, what artwork is, or what a beach is?
We'll have to get creative.
This exercise forces our brains to think more simply, more out-of-the-box, and more carefully about how others might interpret what we're sharing.
Is it more important to get our alien friends to understand exactly what a mechanical pencil looks like ("a metal cylinder that comes to a point on one end that exudes an element which can create markings that we use to communicate with each other") — or to capture the essence of how the thing is valuable ("a useful tool for expressing what I'm thinking or feeling")?
The only right answer is to push your brain outside its comfort zone.