You can build models directly in Tinkercad, but you also have the option to load already existing models using Import. When you're finished working, use the Export option to save your file outside of Tinkercad.
Use the Import option to load already existing files into Tinkercad. Either browse your folders by using 'Choose a File' or drag and drop your file into the box.
Your file must be in stl, obj, or svg format and be less than 25MB.
If your file is larger than this size Tinkercad will give you an error and you will need to reduce the size of your file.
After you've loaded your file you'll get a second window. Here you can choose if your file loads in using Millimeters or Inches. It is usually suggested to load using Millimeters, as sometimes size anomalies can happen when loading using Inches.
You also have the option to change the scale of your model here.
Occasionally a model will load very small. If this happens use the scaling option in Tinkercad to size it up. Once you're happy with your settings click Import to finish loading your file.
Note: Depending on the size of your model it make take Tinkercad a bit of time to upload the file. This is normal.
Tinkercad automatically saves your files to the cloud. If you want to save a copy outside of Tinkercad you must Export it. You have a couple different options when exporting.
Your best bets for 3D printing are to export as STL or OBJ. For printing at the library choose STL. Click on your desired file type and Tinkercad will download a copy to your computer.