Application Specific Integrated Circuit (ASIC). Basically a chip that does one job. Most people use Antminers (by Bitmain) as they are the only ones in the business really. You want something in the Terrahash range of processing power. Anything smaller and it's not worth it. Look on eBay and you will find them or the marketplace on the forum.

You don't need to pay for mining on a Pool although pools take a fee from every block found to support running costs.

Google and YouTube are your friends. There's too much to explain.

You need free electricity and the best ASIC you can afford plus a power supply (ATX usually) of suitable rating to run the ASIC. Then set it up to run on a pool (see the pool section of the forum) and then leave it running. You'll need a BTC wallet for your earnings.