You can create anything you like - as long as it can be cut and engraved from flat sheet materials. See some product examples here
Here is a C02 laser in action:
Color, thickness and surface finish
Are determined by the material you pick, check the options out here: https://make.ponoko.com/materials
You'll need to provide
A 2D vector design file (EPS, SVG, AI or DXF).
This just wants to be a, top down line drawing of the parts you want cut (so no perspective or 3D visuals in there). Here is a screenshot of the file for the cut above: