TinkerCAD is an easy-to-use, browser based 3D design tool for creating 3D printable items: toys, decorations, pieces of jewelry, robot parts, etc. Users are guided through the 3D design process through ‘Lessons’, which teach the basics before moving on to more complex modeling techniques.
This page offers a wealth of tutorials for beginners to learn the basics of 3D modeling with TinkerCAD.