|A Blockchain is a place all Bitcoin transactions are stored. It's basically a file or a database and can be used for other purposes.|
So what is a bitcoin transaction? It is the transfer of bitcoin from one address to another.
But what is an address? An address is like a bank account number where bitcoin is held.
So if John wants to send Mary bitcoin, using a wallet software he enters a send $1 to an address (hopefully it's Mary's).
Every bitcoin transaction ever made is visible to everyone in the blockchain.
You can view them at https://Blockchain.info and even the first transaction ever made. But there is no name associated with it, just an address
One quality of the blockchain is that it can't be changed (immutable).
It's called a blockchain because a series of blocks, created approximately every 10 minutes aand is recorded and connected (chained) to the previous block.
You can also see the first block here
Block 700,000 is here and picture below
A block contains:
A sample transaction is here