How to use the pool?
See Getting Started. You don't need to register.
Fee of the pool?
The fee rate is 1% + α.
The α part is produced by rounding errors, so I can't really predict it. You can track it in the stats page.
The official GPU code is still too slow and needs to be further optimized. You can try running multiple instances of the GPU prover if one instance can't use up all of your CPU and GPU resources.
(At the time of writing, there isn't really a GPU prover for the proving pool. It might come in the future. Remember that it's performance is so bad (comparing with closed-sourced ones) that you are not really losing much.)
The pool uses PPLNS scheme, where N equals 5 x proof target, and share value equals solution target, capped at 2 x proof target. All amounts shown on the website is in testnet credits, so you need to divide them by 5 to get the converted rewards on mainnet.
This is effectively an IOU reward though, so you will need to trust me to pay you in time. In general, as soon as I actually receive the credits, I'll work to distribute them to pool participants, no matter on testnet or mainnet.
I can't find my address on explorers?
The testnet doesn't have transfer capability right now, so you can't find your address on the explorers. You can only see your balance on the pool's website (with yellow top bar). Also, all rewards are not actually sent to prover addresses on the current phase.
Most of them were caused by a bug when the pool server is restarting. The pool server will now reject those solutions, so there should be much less invalid solutions now. I will investigate the new invalid solutions as they appear.
The pool protocol?
The pool protocol is described in the Stratum specification.
The protocol is not encrypted, so keep that in mind if it might be a problem for you.
Unfortunately, the closed-source high-performance GPU provers are not using this protocol, so you can't use them here. Although in theory I could make some of them compatible, generally it's not a good idea to do that.
Originally this pool was called "Haruka's Aleo Mining Pool" during the testnet2 days. As now we tend to use "proving" instead of "mining", it should be called "Haruka's Aleo Proving Pool" now, but I'm already using "HAMP" everywhere, so I'm sticking with it.
... sorry I don't really have a sense of naming.