I understand that crypto currency is a form of digital money like Bitcoin and Altcoins like ethereum, ripple and the rest.
Unfortunately the definition of "cryptocurrency" has been stretched a little. Technically any currency based on cryptography and blockchain technology is a cryptocurrency. But some of them are not currencies at all like ethereum which is a platform for smart contracts (with ether as the fuel for smart contracts).
They can be decentralized like bitcoin or centralized like ethereum, ripple, etc.
While Block chains are decentralised, public digital ledgers used to store crypto currencies and record transactions.
Blockchain is simply a chain of blocks that doesn't have to be public or even decentralizied.
Blockchain is the technology that enables the existence of crypto currency. There is no crypto without Blockchain.
Correct about most projects but not all. For example there are altcoins that use DAG which is a graph (no linear relation like chain).