Anyone can mine pow-givers and receive coins from them.
Before the miner finds a proof-of-work and receives a reward, he needs to iterate over a large number of hashes.
Hashrate - count of processed hashes per second by miners.
Gh - gigahashes (10^9 hashes), Mh - megahashes (10^6 hashes)
Original info how to mine
The easiest way to mine giver contracts is MyTonCtrl, though.