Cryptocurrencies (or coins) are mined by miners (individuals or organizations) using their computing (hashing) power to process transactions and earn rewards. To be more specific, mining is the process of recording transactions to the public ledger (blockchain) with an incentive to receive a miner reward.
This process is very resource-intensive. It requires substantial computing power to meet the cryptographic rules which secure the system and to ensure that all network participants agree the blockchain is valid and accurate. Moreover, as more computing power is added to the network, the difficulty of solving the ‘puzzle’ which allows miners to earn a reward increases – that is where the mining pools come into play.