I don't know how to operate a DOS operating system. Where should I ask networking and computer operating systems questions?
Retrocomputing Stack Exchange is a question and answer site for vintage-computer hobbyists interested in restoring, preserving, and using the classic computer and gaming systems of yesteryear.
Both sites have quite a few MS-DOS questions already:
Stack Exchange sites require that you show prior research. A certain amount of prior knowledge is assumed.
So, if you are a complete beginner you should first learn the basics of DOS. Stack Exchange is not the place for that; instead, find a book or course on the subject.
After that, if you still have a problem, you can ask on Super User. Be sure to search there first; maybe your question has already been asked and answered.
You also mention networking. We have NetworkEngineering Stack Exchange. The same advice applies here: Stack Exchange is not a place where we teach the basics; if you need to learn the basics of networking, there are plenty of websites about that already. If you have a specific question, that has not been asked yet on Network Engineering Stack Exchange, then you can ask it there.