Choose one CAD tool, install it, and design a simple part (5cm × 5cm × 2cm with one hole). Document why you chose this tool and your first impressions. Include screenshots of the workflow and the exported STL.
Don't paralysis-by-analysis. Pick one of Fusion / OnShape / Tinkercad. Try it for 2 hours. Move on if it doesn't work.
Chose Fusion 360 because:
Designed a 50×50×2mm phone-stand-shaped part with a 5mm hole. Workflow: New design → Sketch on top plane → Rectangle 50×50 → Extrude 2mm → Sketch a circle 5mm radius → Extrude-cut.
Time to complete: 25 minutes (first time). Export: STL with 'Custom' tolerance 0.005mm.
Reflection: Sketching was the steepest part. Once I 'got' that I'm drawing a 2D sketch first then making it 3D, it clicked.