Software: Tinkercad
Tinkercad is an easy-to-use 3D CAD design tool. Quickly turn your idea into a CAD model for a 3D printer with Tinkercad.
Installing
There is nothing to install. Just go to https://www.tinkercad.com/, and create an account. It runs in a web browser. If you're not ready for Fusion 360, then give Tinkercad a try.
Step-by-Step Lessons
When you first create an account, it walks you through some step by step lessons. You can revisit them by clicking learn across the top banner.