The transaction initiated from a Bitcoin wallet is transmitted to the Bitcoin Blockchain before being broadcast in Peer-to-Peer mode to all nodes on the network.
When a node receives a transaction, it will check if it is valid.
The node then decides whether to accept or reject this transaction.
You should be aware that the nodes of the Bitcoin Blockchain are a critical part of the infrastructure that allows its network to function properly.
2.1 Simple Nodes
Simple nodes can be online or offline.
When a simple node is online, it will receive, save and broadcast all the latest transaction blocks to all the other nodes in the network whether they are online or offline.
When an offline node reconnects, there is a synchronization phase with the Bitcoin Blockchain during which the node will download the missing part of the Blockchain.
Masternodes are nodes that are equipped in a slightly more important way than simple nodes.
A masternode will work 24/7.
Running a Bitcoin masternode will require specific equipment since it requires a lot of resources: power, maximum availability, maintenance, disk space, and RAM memory.
A masternode therefore always has the most up-to-date version of the Bitcoin Blockchain.
The more masternodes a Blockchain such as Bitcoin has, the safer and more secure the Bitcoin Blockchain is.