Cryptocurrency mining is a two-way process.
1. One, it is an accounting process to verify, validate, and record cryptocurrency transactions on an online, public, and encrypted ledger - called the blockchain. This is done by installing a CPU/specialized computers, called miners, along with the verification software of the cryptocurrency.
2. Two, it is also the process for minting new coins and bringing them into public circulation. This is also done to incentivize or reward those who install their computers for the purpose laid out in point 1. Mining is usually a voluntary activity. Hence incentivization plays a big role in it.
In short - a cross between an accountant and a gold miner.
There are multiple types of mining CPUs depending on the type of coin or token being mined and the consensus mechanism being used e.g. Proof of Work or Proof of stake etc.
There are roughly 500 mineable coins or tokens today.
I hope this helps.