A web server is a program that uses HTTP to serve files from web pages That an HTTP client has requested. A web server is a client/server model and all websites have to be on a web server. Most computers come with web servers with email and FTP programs in them.
A WAN is a wide area network that can be used by one organization or everyone. It is a LAN that covers more space. The internet is a WAN
An LAN is a local area network that supports a small network that could be in your home