To create a network, you need nodes and the connections (also called links) between them. Connecting nodes means creating some sort of temporary or permanent connection between them. Over the past decade, wireless connectivity has become one of the most popular ways to do this, especially at home. Wired connections are still common in offices. 

Besides computers, peripherals, and connections between them, what else do you need? Each node on the network needs a special circuit called a network card (more formally a network interface card, or NIC) to tell the node how to interact with the network. Most new computers have a network card built-in by default. If you have an older computer or laptop, you may need to install another breadboard (or add his PCMCIA card to your laptop) so that your computer can communicate with the network. Each NIC has a unique numeric identifier called a MAC (Media Access Control) code or LAN MAC address. A MAC code is a bit like a phone number.
Each machine on the network can communicate with another machine by sending messages with MAC codes. Similarly, you can use MAC codes to control which computers on your network can access files and other shared resources. For example, his wireless connection to the Internet was set so that only two MAC codes could access it at a time (thus limiting access to the network cards built into both computers). This prevents others in nearby buildings (or streets) from hacking or accidentally using my connection.

The bigger the network, the more parts you need to add to make it work efficiently. Signals can only travel through wired or wireless connections. Therefore, if you want to build a large network, you need to add devices called repeaters, or signal boosters. Bridges, switches, routers, etc., connect networks (or parts of networks called segments) to each other, regulate traffic between them, and regulate traffic from one part of the network to another forwarding part. You may also need a device to help you. 

Understanding computer networks with layers?

Computer networks are similar:
we all have different ideas about them and care more or less about what they're doing and why. If you work in a small office with your computer hooked up to other people's machines and shared printers, probably all you care about is that you can send emails to your colleagues and print out your stuff; you're not bothered how that actually happens. But if you're charged with setting up the network in the first place, you have to consider things like how it's physically linked together, what sort of cables you're using and how long they can be, what the MAC addresses are, and all kinds of other nitty gritty. Again, just like with computers, we can think about a network in terms of its different layers—and there are two popular ways of doing that.

The OSI model
Perhaps the best-known way is with what's called the OSI (Open Systems Interconnect) model, based on an internationally agreed set of standards devised by a committee of computer experts and first published in 1984. [2] This describes a computer network as a stack of seven layers. The lower layers are the layers closest to the computer hardware. Higher levels are more like human users. And each layer allows what happens in higher layers:

Physically:
The underlying hardware of a network, including cables and connections, and how devices fit into a particular network topology (ring, bus, etc.). The physical layer has nothing to do with the data that the network transfers, and is irrelevant and irrelevant to most human users of the network.
Data connection:
This includes things like data packing and error detection and correction.
Communication network:
This layer deals with how data is addressed and routed from one device to another. shipping:
It manages how data traverses the network efficiently and reliably, ensuring that every bit of a given message is sent correctly.
meeting:
It controls how temporary "conversations" (sessions) are established so that various devices on a network can exchange information.
presentation:
This effectively transforms data generated by easy-to-use applications into a computer-friendly format for transmission over a network. For example, compress (to reduce the number of bits and bytes transferred), encrypt (to keep data secure), or convert data between different character sets (to make emoticons (“smileys”) and emoji readable). to ensure that in your email).
application:
The top of the model and the one closest to the user. This includes things like e-mail programs that use the network in a way that makes sense for a human user and does what the user wants to accomplish.

More info:  Computer network