How do offchain transactions get validated/confirmed whilst using Lightning network? How do offchain transactions get validated whilst using Lightning network?
Individual transactions on the lightning network will never be confirmed on the blockchain.

However, the net sum of value passed back and forth on a single channel (regardless of how many lightning transactions that is) will be validated on the blockchain as part of one closing transcribe for the channel.  This is similar to how money is transferred in the traditional financial system using a process called "deferred net settlement".