I have a Prusa i3 MK2S printer. I chose the build your own option to save a bit of money and get to know the printer a bit better. It was worthwhile and the user comments in the online build manual were invaluable.
Like all CAD packages, FreeCAD has a bit of a learning curve. My go-to resource is this excellent tutorial which covers everything I need to create a basic part.
Engraving or creating raised text on a design is very common. The standard tutorial is here which I found a bit complex. However, at the end of the tutorial, there is a reference to this thread which talks about binding a 2D draft object to a surface. Go with the flat face option and when extruding and choose reference rather than one of the copy options.
Once you’ve created your design in FreeCAD, select the Body in the tree view that represents the entire part.
Using the File pulldown menu, select Export.. as an STL file.
Import the STL file into the slicer program. Adjust the desired print resolution and fill settings.
Export from the slicer as a GCODE file and copy that file to the printer’s SD card.