To put it simply, a blockchain is a digital ledger or a list of transactions that can be viewed and verified on the internet.
Transactions are grouped together in blocks and then processed with a unique block number and time stamped.
These blocks follow each other sequentially like a chain and therefore is called a blockchain.
In fast blockchains these blocks are created every 5 seconds and in slow blockchains the blocks are created every 10 minutes.
You connect to the blockchain with a wallet.
The blockchain thus holds a record of every time someone sends or receives a cryptocurrency on a secure blockchain network.
Computer nodes across the world are connected to the blockchain.
These computer nodes hold a copy of every transaction ensuring the verification and transparency of transactions.
As these blocks continuously move forward and cannot be stopped, cancelled or reversed transactions are immutable.
Blockchains provide a number of advantages such as secure payments, privacy, global networks, and transparent record of transaction history.