Building physical prototypes of products used to be a very long and expensive process. However, 3D printers allow people to make their ideas come to life much faster.
Tinkercad is a free online software to design your 3D model. After finishing your design, save the model as a .stl file. This is a file type that stores you model for printing.
Next, install the software Cura. This software uses the stl file from Tinkercad to talk to your 3D printer. Inside Cura, you can load your model file. You can also resize your model and select the nozzle size for printing. The printer works by using a pen filled with melted plastic to draw your model, like a frosting gun but less tasty. A large nozzle means the model is completed faster, but makes the final product look like it is made of spaghetti. A smaller nozzle makes a much smoother product, but takes significantly longer to produce.
Inside Cura you can also get an estimate of production time, usually several hours. If the number is large such as 20+ hours, your model is likely too large or solid, etc.
Lastly, you can save the Cura file to a flash drive. Then, insert the drive into your 3D printer and wait for the model to be completed!