what is the responsibility of the network/server of a company? (lets say that it's a retail company)?

Answer 1

That depends on what you are using it for. You don't use one server for everything. If you do and it goes down you are out of business. There should be a Web server, a domain controller, a file server, mail server, a gateway, etc. There are a lot of different things that you need for a business. Look for a plan and go from there.