Greetings,
STL is just a 3d CAD file format, not code. Just as 2D CAD packages produce DXF files to feed into a CAM package for conversion to G code, 3D CAD packages produce some 3d model format (OBJ and STL are two common file types in the 3d printer world) to feed to CAM. The slicer produces the G Code that is fed to the printer FROM the stl file.
A slicer is just a CAM program that works in layers for additive "machining" while a CAM for subtractive 3D machining produces G code for machining away unwanted material. Build an object up from a plane vs machine away everything that isn't the wanted object working downwards. At least for most conventional 2D, 2.5D, and 3D milling operations...
To avoid unpleasant surprises for those new to this, STL models are made up of triangles. They are not smooth surface models. In most cases, the triangle count is high enough and the created object is small enough this is irrelevant. The model detail is higher than the process resolution. Watch out for low polygon count models, they are sort of trendy in a minimalist fashion, rather in the way the Tesla pick up is a very planar looking vehicle.
If you scale a tiny low resolution model up to a large size and 3D print it, you may see uneven surfaces and the triangular surface structure can become visible. Similar to a subtractive machining post processor/CAM package that processes arcs as a series of straight lines connecting the points of an arc, you can end up with faceted curves. This may or may not matter or even be readily visible depending on how close the connected points are along the curve.
If you want a quick overview of various 3D file format standards, have a peek at:
https://www.capvidia.com/blog/top-neutral-3d-cad-file-formats
Some of these file formats are not typically used in the small hobby shop sort of world, but it's always interesting to know what's out there as you may find a model in several formats your software can import and each format has strengths or weaknesses.
Cheers,
Stan