To verify nothing gets tampered with, every block shops the hash of the block earlier than it. That way, if there’s ever a discrepancy between the 2 locations the hash is saved, you’ll know something’s gone wrong (more precisely, your pc will know — you don’t have to manually verify the chain yourself). If you had to visualize what a blockchain really seems like, think about a bunch of receipts ordered into bins, which are all tied collectively.