Mining bitcoin or other altcoins has two purposes. The first is to confirm transactions and validate blocks, and the second is the creation of new coins. In practice the miners use powerful computers to solve complex mathematical equations that “unlock” transactions in a block, allowing them to be added to the blockchain. This is called a Proof of Work consensus method, and only Proof of Work blockchains use mining.
An application-specific integrated circuit (abbreviated as ASIC) is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. In Bitcoin mining hardware, ASICs were the next step of development after CPUs, GPUs and FPGAs. Capable of easily outperforming the aforementioned platforms for Bitcoin mining in both speed and efficiency, all Bitcoin mining hardware that is practical in use will make use of one or more Bitcoin (SHA256d) ASICs.