Every block has a portion called the block header which serves to append assembled transactions to the ledger. The block header contains several key fields including a merkle root, a hash corresponding to the previous block in the chain, a timestamp, and a nonce. The hash corresponding to the previous block along with the timestamp allows us to see precisely where in the blockchain this particular block belongs.
The merkle root is a singular hash made up of a long tree of hashes that are paired up and combined in order to create a hash that puts them together. For example, Hash2 and Hash3 are combined into a new hash called Hash23. This process repeats until there is only one remaining known as the merkle root. If the branches are traced back, one will be able to see the transactions that have been confirmed. There is also a nonce which will be used to refer back to this block in the future of the blockchain. Since it is also hashed, it gives a method to ensure that the block has not been altered.