I'm still trying to understand what I can do with curves and what the limitations are.
It's a closed shape. Once I have this shape, I'd like to be able to extrude the shape, like I can with a circle mesh, to make a tube in the shape of that curve. I've read this answer, which is pre-2.9, so some of what it includes is not doable now. (Or is, but I don't know how to do it.) I know I can convert it to a mesh, but is it possible to take this shape, made out of bezier curves, and make a tube or prism from it without turning it into a mesh?
EDIT: After one answer, I think I should clarify: This is a closed curve and, rather than have something like a tube that follows this curve, I want this curve to be a cross section for a tube or prism.