Here’s a link to a superb video that shows how to create a 3D Model (.stl file) from a 2D drawing.
The process takes 5 minutes or less once you’re familiar with the tools.
He uses just 2 pieces of software, both free:
– Inkscape: https://inkscape.org/en/ (a vector graphics editor)
(BTW, only download these programs from the official .org sites)
These programs are standards in the modelling world: widely used and best in class.