In the early days of the computer age, information and calculations were stored and performed mainly locally. With the development of protocols and communication technologies, people began to create computer networks. The basic concepts that should be known to talk about networks are: Network - a set of related nodes that exchange information among themselves, Node - basic network unit, user or computer, Server - a node that is connected to a large number of other nodes.

As you can see in the picture, we can distinguish three types of networks: Centralized, Distributed and Decentralized. In a centralized network, there is one master server that sends data to other network nodes. All nodes communicate via the central node. When the central server fails, the network stops working.

In a distributed network, there is no central node, and all nodes communicate with each other using the shortest possible paths.
A decentralized network is a combination of a centralized and distributed network. There is no one main server in it, however, we sometimes distinguish special nodes called the master node. These differences are best illustrated by the picture above

Bitcoin uses the architecture of a decentralized network. Each of the network nodes stores a copy of all performed operations. To group an operation, they are saved in the form of blocks, which can be identified with subsequent files where each subsequent file indicates its predecessor. This is best seen in the picture above. The existence of as many nodes as possible of the bitcoin network is important for its stability because they verify and validate the entered data.

Finally, I would like to explain one important thing that is often repeated and is not true. Very often the concept of distributed ledger is put on a par with the blockchain. That's not true. Distributed ledger technology (DLT) is a broader concept than blockchain, which is just a kind of distributed database.