Decentralized networks are made up of computers, or nodes that interact in a peer to peer system with no third party involved. Nodes are network stakeholders that can be ran by individuals and corporations to further support the network. Each node downloads every block and transaction history checking them against the bitcoin consensus rules in order to maintain the integrity of the blockchain. If a transaction or block violates one of Bitcoin's consensus rules, a node will automatically reject it. This helps to solidify and protect the digital ledger from fraudulent transactions while validating legitimate transactions.
Setting up a node does not have to be complex, while there are many companies selling nodes you can also create one with a raspberry pi that has node specific software such as Umbrel. There are two fundamental types of nodes; a full node and a lightweight node. A full node downloads a complete history of every transaction that has ever been executed which is about 350 GB on the bitcoin blockchain network. If you run a full node, you rely on your server to broadcast transactions to the network. A lightweight node only downloads the essential header data, they are typically used as wallets and connecting to full nodes. If you don't have a lot of processing capacity or are looking for a more cost-efficient way to run a node a lightweight node. They are ideal for nodes that don’t have a lot of storage or processing capacity and are more cost-efficient to own than full nodes.