Is there a blockchain explorer up and running for YAC yet?
Not yet, someone had said they were working on it so I haven't bothered. If nothing materialises soon I'll get on it.
"Can be mined" by who? Me mining solo, me mining in some remote pool or anyone?
What's Stake or Proof-of-Stake?
Stake/Proof-of-Stake is term referring to the use of currency itself (ownership) to achieve certain goals. In NovaCoin proof-of-stake is used to provide minting and transaction processing in place of proof-of-work. Please refer to our design paper for details of this approach and our implementation.
The 'stake' field in the getinfo output shows the currency amount you currently staked to protect the network. This amount is subject to the holding period of 520-block maturity window before you can use it again (it would return to your balance once matured).
When can I start generating proof-of-stake blocks?
After 30 days the network would start seeing proof-of-stake blocks. If you have balance novacoind would automatically try to generate stake for you. If you find a stake the reward is calculated using current proof-of-stake difficulty and coin-years amount consumed. The reward amount is added to your stake amount and is shown together in the 'stake' field of getinfo output.
Because stake is withheld from spending for 520 blocks, if you do need to keep your balance around to be spent soon we provided a configuration option 'reservebalance' to help you keep your balance from being used by stake. You can add a line 'reservebalance=10000' to novacoin.conf and restart your novacoind. This way novacoind would try to keep your balance above 10000 coins when generating stakes.
To clarify, you have to leave the coins dormant for 30 days, and then they are eligable for proof-of-stake minting. If you have yacoind running, it will happen automatically, otherwise it will happen when you run the daemon.
There's a detailed Windows PPC proof-of-stake minting guide which is obviously relevant to YAC too -
https://bitcointalk.org/index.php?topic=187714.0