3-D models are freely available at various websites. Tinkercad contains a gallery of 3-D models. The gallery items can be modified or printed. However, not all models are perfect for printing. Some items in the gallery are better for viewing only as the models are extremely large or impractical to print.
Other models are available at the following websites:
Please be advised that models obtained from websites may have copyright restrictions. For more information regarding this topic, view the "Copyright, citations & terms of use" page located at the tab above. To learn more about 3-D printing, view the PBS video below:
For beginners, Tinkercad, a 3-D software package from Autodesk, is a good place to start as the product is free and easy to use. The Tinkercad website also contains many pre-created models. The models are available with creative commons licenses so the items can be modified or printed.