It is possible to generate a model for 3D printing in a variety of ways, including downloading existing models, scanning real-world objects or designing your own model.
There are a number of online resources for people to share, download, and even print 3D models:
The most common files for 3D printing are .stl and.obj (including color information for advanced printing). While there are sites to purchase 3D printable files, these sites listed below have robust communities that share their models for free:
If you'd like to produce a 3D model of an object that already exists, Photogrammetry and 3D scanners offer options, though models might need to be edited to fix design or mesh issues.