“All this slicer stuff”:

So an STL file stores the shape of an object by defining triangles by their vertices in 3D space. Kind of like a giant 3D connect the dots puzzle. I’ll note here: This is a close but imperfect approximation of a shape, especially curved surfaces are actually highly faceted. Other file types like AMF or 3MF or something might be able to do true curves, I’m not sure. An STL only stores the surfaces of an object, it is up to the program that is reading it to interpret the interior as hollow or solid or whatever.

Your 3D printer can’t understand an STL file. It’s a fairly simple machine, it’s got a couple heaters, a couple fans and a few motors, and it needs to be told what to do with them in very direct terms. Most 3D printers use a command langauge called G-Code for this; a line of G-Code might look like this: G1 X35.386 Y181.683 E27.01397 I actually copied that line out of a G-Code file. It’s commanding the printer to move the nozzle from its current position in a straight line to an X, Y and E position. E is the extruder axis, get used to that 3D printers actually track motion in 4 axes. G-Code is designed to be human readable and writable, and I suggest you learn a little bit about how it works for reasons I’ll get to later, but for the most part you’re going to use software to automatically generate G-Code, using a slicer.

A slicer is what we call 3D printer CAM software. 3D printers usually create objects by laying down thin, flat layers of plastic that can be described in 2D terms, so the software “slices” the model into a bunch of horizontal cross sections to arrive at a 2D shape, and then uses an algorithm to draw that shape using lines of extruded plastic. G-code has commands for curves and such but most slicers just use a series of very short straight lines.

The general algorithm is going to be something like “draw a few laps of this layer’s outline. Color inside the lines, and then move the Z axis up a fraction of a millimeter and do it again.” Things like how many laps it does drawing the outline, how densely to color inside the lines and in what pattern, along with what temperatures to heat the bed and nozzle among many other things are adjustable in the slicer’s settings. Almost all of the 3D printer’s behavior is actually decided by the slicer.

Including the little routines it goes through at the very beginning and end of the print. You’ll find a page in the settings that allow you to write custom G-Code that it will copy paste at the beginning of each file, at the end of each file, and sometimes between each layer. I have a Prusa-style bed flinger printer, and I added a command to the end script to run the bed all the way forward as if presenting the model, to make it easier to get to for removal. This is why I said it’s wise to learn a little about G-Code, so you can add customizations here.

Additional tools: I like to keep a pair of needle nose pliers near the printer to grab oozed filament, some side cutting pliers for snipping filament, I have some dedicated allen wrenches for the common adjustments on my machine, and a razor scraper for removing prints from the bed. Your machine may have different features than mine so adjust accordingly.