A block contains transactions. Multiple blocks referencing each other form a blockchain, a distributed database that contains all transactions ever conducted on a certain cryptocurrency network, for example bitcoin. Transactions and blocks are confirmed using cryptography and a hard-to-solve task (proof-of-work which discourages fake blocks altho there are other anti-counterfeiting systems) and those signatures can be verified by anyone which makes the blockchain work without a central authority.

This should give you enough to get started searching for other information that may interest you.