Blockchain uses the concept of Merkle trees to store the hashes of information. Example Bitcoin uses Merkle trees to strore hashes of transactional data, while Ethereum uses Merkle Patricia tree structure. Where Mekle trees does is, it hashes the transaction and generates a root hash of them.
The branches consists of the hashes going up along the path to the root. Noe suppose there is a large database, the data of which is stored in a merkle tree. Now, if the root of the tree is publicly known and the user wants to retrieve the data based on the key-value pair, he can ask for a merkle proof and upon receiving the proof he can verify the position of the data.
Let's talk about the Ethereum: In Ethereum, every block header contains three kind of Merkle trees. a tree of transactions, tree of receipts and a tree of state Now, the three different trees account for getting a verifiable answers to many queries.
Since state in Ethereum consists of a key-value map where the keys are addresses and the values are account declarations, listing the balance, nonce, code and storage for each account . Since the state needs to frequently updated, the keys in the storage are frequently inserted and deleted and also new accounts are updated.