There are basically 3 types of networks:

LAN stands for Local Area Network.

Used in small geographical area to exchange files and messages

WAN stands for Wide Area Network

It is the interconnection of various LAN’s

MAN stands for Metropolitan Area Network

It is the interconnection of various LAN’s in metropolitan cities.

OSI Model Networking

The Open System Interconnection Reference Model (OSI Reference Model or OSI Model). It is a seven layer reference model to standardize communication networks. The layers include as stated in diagram below:
 

 


Application Layer: In this layer we identify the user who wants to communicate, check whether the data and networks sources are present and synchronize the communication between the two users.

Presentation Layer: As names says itself, we present the data in a way that could be easily recognized by the application layers of other end users.

Session Layer: The main function of session layer is establishing, maintaining and ending the connection between two users.

Transport Layer: The transport layer work is to deliver the data or the messages between the two users.

Network Layer: It is responsible for handling errors, controlling network, packet handling, congestion handling and addressing.

Data Link Layer: It provides consistent transmission services to the network layer.

Physical Layer: It is the layer that deals with the physical components of a network.

 
How to share internet connection between two computer systems
 

Connect the two computers with CAT5 Cable.

After connecting both the computer systems, assign a different IP addresses by going in the properties of the LAN card like 200.200.200.3 and 200.200.200.4 or any other IP address. These ips are private.

After assigning the IP addresses install software on first computer, which will be used for sharing the Internet connection and this is said as proxy software. The most common proxy software is ICS which is by default installed in Windows operating systems and can be configured separately.

We can install a hardware router, which will be act as a gateway. Your router will be connected with the public IP address, which will be assigned  by our ISP and hub will be attached to the router. All the computer systems in your homewill be directly attached to that hub.