A Blockchain is a digitized, decentralized, public ledger of all cryptocurrency transactions. Constantly growing as ‘completed’ blocks are recorded and added to it in chronological order, it allows market participants to keep track of digital currency transactions without central recordkeeping. Each node (a computer connected to the network) gets a copy of the blockchain, which is downloaded automatically.
A block is the ‘current’ part of a blockchain, which records some or all of the recent transactions. Once completed, a block goes into the blockchain as a permanent database. Each time a block gets completed, a new one is generated. There is a countless number of such blocks in the blockchain, connected to each other (like links in a chain) in proper linear, chronological order. Every block contains a hash of the previous block. The blockchain has complete information about different user addresses and their balances right from the genesis block to the most recently completed block.
Finding and publishing new blocks is what Bitcoin miners do to earn bitcoins. Whenever a new block is broadcast, approximately every 10 minutes, a quantity of bitcoins is received by the miner who solved that block. Bitcoin miners keep the network secure, and this is how they are rewarded. This system ensures that all transactions are valid, and keeps the bitcoin network secure from fraud.
You can find any transaction or a block here: https://blockchain.info/