The first 50 BTC were generated from the genesis block (the first block in the Bitcoin blockchain) which does not reference previous blocks.
There is some fantastic technical information about the genesis block here: https://en.bitcoin.it/wiki/Genesis_block
https://bitcoin.org/en/developer-guide#term-genesis-block

As with all other blocks, you can view details about it using a conventional block explorer: https://blockchain.info/block-index/14849