What is a blockchain & how does it work? Why blockchain at all?

Blockchain is a database of the transaction history. This transaction history is stored inside a block, these blocks contain information regarding the previous block thus linking them together to create a chain of blocks, otherwise known as a Blockchain.

Blockchain is widely used due to two main reasons, blockchains are decentralized - this means there are no 3rd parties involved in approving your transactions on the chain, this also means blockchain is immutable (Tamper Proof) as they rely on all parties in the network agreeing on the blockchain (This is known as consensus).

Blockchain is highly secured due to its use of cryptographic keys and signatures - this prevents fraud such as other users pretending to be you as they would not be able to replicate your private keys.

If you're interested in the technical details of miners' fees, read Jeff Coleman‘s Stack Exchange post

What is meant by the term "gas"?Ethereum Stack Exchange