Here is the source file for extrusions. https://git.blender.org/gitweb/gitweb.cgi/blender.git/blob/refs/heads/master:/source/blender/bmesh/operators/bmo_extrude.c
You should be able to set some debug points in your build environment to inspect it step by step a bit more. Just keep in mind that blender is a production product with a lot more going on in order to support more complex models/data. While it is more commented there will also be a lot more boilerplate code.
Learning from it is fine but just remember: If you are building your own or working on someone elses project DO NOT use any snippets from blender in outside projects! (unless the file doesn’t fall under GPL and you are able to comply with it such as an external library or a part of cycles).
Hopefully that helps.