I watched the video but did not get it the reason why 1st transaction has no input in a block?
Anyone can explain more?
Assume we’re talking bitcoin 
. It’s the “coinbase” transaction, which is how new bitcoin are produced (currently) as a reward to the successful miner for securing the blockchain. It was created programmatically according to a well-known emission schedule and wasn’t the result of a previous utxo being spent, so no input. cheers