http://investst6kbbg2u3prbitqmt3ryxaghgksnpzsqj22y63tvwhnolgrad.onion/bitcoin-maining/index23.html
What they're actually doing is trying to come up with a 64-digit hexadecimal number, called a "hash," that is less than or equal to the target hash. Basically, a miner's computer spits out hashes at different rates—megahashes per second (MH/s), gigahashes per second (GH/s), or terahashes per second (TH/s)—depending on the unit, guessing all possible 64-digit numbers until they arrive at a solution.