The transaction is added to the blockchain and deemed "confirmed" if it successfully completes all validation checks. I hope this makes it more clear how nodes validate or confirm transactions on the block.
Wrong.
As I said in the first reply, transactions are confirmed by miners.
Transactions must be valid, so that they can be included in the blockchain, but it's not that a transaction is included in the blockchain once it's validated.
For a transaction to be included in the blockchain, it's required that a miner (or a mining pool) solves the proof of work problem, mine a block and include that transaction in the block.