1. You don't need to setup bitcoin. All you need to do is download a wallet that works best for your needs and be sure to encrypt it so as not to be prone to any hacks whatsoever.
2. A bitcoin miner works like a problem solver (lol); 1 puzzle is created every 10 minutes, and for miner to correctly solve this puzzle correctly, it needs to be fast and able to do lots of predictions in a short span of time in order to get the answer on the puzzle. Once the puzzle is solved by this miner, the puzzle piece would then be connected into a chain of puzzle pieces (blockchain) and this recently solved puzzle would be the basis to the next puzzle being generated.
3. You need an ASIC miner in order to mine for bitcoins. Computer processors and GPUs won't take the cut as a huge amount of power is necessary to be able to get something out of your mining endeavors, and ASICs are programmed and designed by just mining bitcoins and nothing else.
4. A bitcoin miner basically process transactions in the whole network and that is their main work in the bitcoin ecosystem.