This slicer ships with, and is recommended for, the Prusa line of 3D printers (when you click to print something in your 3D design software (e.g. Fusion 360) it sends the 3D geometry to your chosen slicer software, that software drives the actual printer). Simplicity and the exact visual reproduction of the printed bed make this a good choice for slicing (slicing is the mathematical process of cutting a 3D object into layers that can be printed successively). Another advantage is that online help for this printer will generally assume the use of this slicer. There are a myriad of settlings and parameters that printing software must respect to adapt to each type of 3D printer and the pairing of the Prusa printers with this slicer will be the best.
Simplify3D knows how to convert the 3D geometry generated by Fusion 360 into G-Code (shown in the black text window lower right). I have just told Fusion 360 to print this and it automatically launched this and passed the 3D geometry to it. Simplify3D is a "slicer" because it knows how to convert a 3D object into slices that a 3D printer can lay down (one on top of the other). Simplify3D is fairly expensive and competes with a number of free products (like Slic3r, Cura). It gives me a 3D view of the object and enables positioning and rotating it on the bed and configuring dozens of parameters. It is about to deliver the G-Code (via a USB connection) to my RepRap 3D printer (although it is often preferable to use the "Save Toothpaths to Disk" button to generate G-Code and write it to an SDCard which the printer can accept). The black text-edit window shows what the G-Code looks like. It is just text. With hundreds of thousands of commands that mostly move the head to successive X-Y positions and a defined filament feed-rate.
Expensive and cheap RepRap printers have the same type of control panel. The info-screen displays on startup and during print jobs, it shows the temperature of the nozzle and the bed and percentage completion. Pressing the dial-button brings up the menu, you move the selector by turning the dial and select a choice by pressing it again. An SD-Card inserts on the side (that is where you write G-Code files produced by your slicer software). Then, using the "Print From SD" menu choice (bottom panel), you choose the desired file and click the button to begin. That initiates the head and bed heat-up sequences and the print starts when that is done. This control panel is also needed to load and unload filament, calibrate the height of the bed, settings, etc.
Czech inventor, Josef Prusa, takes great pains to preface the name of each model with the word "Original" (e.g this is an "Original i3 MK3S"). Dozens of Chinese companies have copied his i3 machines and sell them for 1/3 to 1/2 the price. But buyers must deal with no support, disconnects between absurdly poor instruction manuals and parts, poor quality parts, parts that do not fit or work, no wonder that a large percentage are never able to complete the assembly. This printer, by contrast, has a LEGO-quality instruction manual and lots of online support. It also has auto bed levelling (this is a huge factor), much better cable routing, automatic filament insert, removable flexible bed, has its own slicing software, it prints faster, is quieter, does not break down all the time and print quality is much better (note the closeup: less than 1mm thickness, yet highly precise). You can even pull the plug out of the wall during a print and it will continue after reconnect! And its updates its software through the slicer software (super important to new).
3D Design software has revolutionized traditional ceramic manufacturing, now it is accessible to hobbyists and potters.