When we add a transaction to a blockchain, aren't all the transactions hashed? Once we do that and keep on adding hashed blocks, how are we able to look up any transactions and their details?
When a transaction is broadcasted, the raw serialized tx is broadcasted. This includes the inputs, outputs, and signatures. The transaction hash is actually the hash of this serialized tx.
When blocks are mined, they simply include a block header, plus the serialized transaction data for each transaction in that block. Once again, the block hash and tx hashes are the hashes of the block header and the serialized txs.
Since the serialized data contains the inputs, outputs, and signatures, it is possible to view the history by simply going through the blockchain.