I need more explanation because I still don't understand how a node confirms a transaction and determines whether a block is valid, it seems too complicated.
Transactions are not confirmed by nodes. Transactions are confirmed by miners.
Take note that confirmation means being included in the blockchain and that's different from being validated.
A miner (or a mining pool) that manage to find a block, sends the block to the network. Nodes receive the block and validate it.
Validation of a block means checking if the block and the transactions included in that are valid.
[/quote]
Let’s not forget that miners are really just a specialized type of node.