So now that you understand the what a blockchain is, I'll mention the three main types of blockchains -- Public Blockchain, Private Blockchain & Consortium or Federated Blockchain.
A public blockchain is exactly what its name suggest, public. Everyone has access to it, anyone can write to it and anyone can audit/ verify information on the blockchain. There exists no central entity to control the flow of information in any direction. Public blockchains are openly built and supported, making it the highest level of trust that can exist within a network.
If no one entity controls the blockchain, how are decisions made? Decisions within a public blockchain are made via hard coded decentralised consensus mechanisms built into the blockchain. The two most common mechanisms are proof of work(POW) and proof of stake (POS). To change any mechanism within a blockchain, the code needs to be modified and this is referred to as a fork.
A private blockchain is exactly what its name suggest, private. Access to this blockchain is controlled by a central entity whose given the power. In order for someone to read, write or audit the blockchain, the central entity has to allow that person access to the blockchain.
Decisions on this private blockchain are subject to the central entity controlling it.
A consortium or federated blockchain combines different elements of both private and public blockchains. It isn't controlled by one entity, but rather a group. This group makes decisions that affect the network and they allow access to select members.
While there are different types of blockchains, their use and applications differ based on desired goals. Privacy and measured control favour the private and consortium blockchains, while those requiring open trust favour public blockchains.
Which blockchain do you think will win longterm?