Step 1: You have to model an object first. What software you use is completely up to you. The OP referenced Tinkercad, which is an online "buijlding block" style modeling tool which can export STL files. That's the trick. If you modeling software will produce an STL, you're good.
Step 2: You need to "slice" the model into layers that the printer can then lay down one layer at a time. I use the Prusa version of "Slic3r". It's free and has been taylored to the Prusa printer. The original version of "Slic3r" is fine too but you have to figure everything out on your own for your particular printer.
There are slicers that cost money, some people love them, some people hate them, your mileage may vary.
