A node is a copy of blockchain used by a member of a separate network. In fact, this is a user’s device, which supports the blockchain.
There are two types of nodes — for blockchain validation and for mining.
The mining node contributes to blockchain by “guessing” the cryptographic key — the hash — thereby confirming each block in blockchain and creating new coins. If it is the Bitcoin network, then the miner earns new bitcoins. Since mining requires powerful equipment and a lot of electricity, you have two options: either create blocks on your own or join the mining pool. Thousands of users with less powerful computers unite their efforts and share the reward among themselves.
The validation node is a confirmation of blockchain on a volunteer basis. That is, you do not guess the “secret code” or hash, but only save a blockchain copy on your device. This is important for maintaining the decentralization of any network because validation nodes have the right to vote on new protocols and other crucial changes.
Volunteer validation nodes are becoming increasingly rare because you need more than 150GB of memory, at least 2GB of RAM and constant access to the Internet. However, they are the key to real decentralization. At least for Bitcoin.