A blockchain is a record of every transaction that can be publicly verified. Each transaction detail will be distributed to all miners on the bitcoin network with a request to be added to the next block. In the meantime, check out the Cryptocurrency ATM Locator service if you wish to trade in Cryptocurrency more conveniently.
In order for a miner to be paid for the work of adding a block, there are two things that have to happen: they have to make sure the hash is valid and the block is recorded in the blockchain. The first condition is purely a technical challenge, while the second condition will force them to examine all possibilities. If the blockchain contains invalid transactions (for example, someone commits a transaction with coins that they do not have), then the next miner who gets a shipment from the miner will refuse so he does not get paid. Therefore the miner will check each transaction to ensure validity before adding it to a block.