E.g. I could: Draw 2D plane 10x10 mm; extrude; on one surface, create a diagonal helper line; put three circles on that line; define diameter of one circle to be 2.5mm; constraint diameter of the other circles to be equal to the first; split the helper line at every circle intersection; constrain all line segments to be equally long - now all things are fully constrained. Negative extrude the circles (e.g. make holes into the first volume).

Should produce something like this:

   *---*
   |o  |
   | o |
   |  o|
   *---*

As sibling comment says, the design is saved as an STL file, a format they all use, which basically describes the shape of your print in a (variabally sized) load of triangles.

However, most use 'slicer' software on the computer as an intermediate step between the STL export from whatever CAD software your using before actually sending (specific instructions for your model) to the printer.

So, if you wanted to print directly from an iPad, my guess is that you'd need a model of printer that 'slices' STL itself, without desktop software. Even then, you'd probably need (a Lightning <-> USB adapter and) a USB drive to actually get the file from iPad to printer.

Other than that, there’s likely a bunch of parameters that control the actual printing process— there are a lot of tradeoffs to make between print speed, material usage, part strength, etc. The printer software will ask you about these before starting a print.

https://en.m.wikipedia.org/wiki/STL_(file_format)

Not quite. The STL is the model. A slicer “slices” the model into tens to thousands of layers and creates a GCode file that tells the printer exactly what to do.

I made a video about it here.

https://www.youtube.com/watch?v=PDeCltdVU3w&t=1s

I personally use Inventor, and there's a nice easy way to convert to STL's in the application.

You then take your slicer of choice (Cura is popular) and toss the STL in there, and click print.

Pretty close to plug & play.

I've setup everything once about 2 years ago, and should probably update the toolchain (klipper is awesome).