If you've never used cad software, I would start with tinkercad. It's browser-based, fairly intuitive, and free. Has some big limitations, but will get you started on your journey. The upgrade path from there is up to you. Calibre, freecad, fusion360, solidworks - all have their fanbase, as well as pro's and cons. If you are a software engineer, the next one I would recommend is openscad - lets you design by coding. This is especially good if you want to build a "template" like a nose cone of a rocket, then just change some variables to make lots of different shapes.