Hi, yeah I'm actually in the middle of writing up an explanation/tutorial.
It works the same way most sites do.
So for Blackjack a deck is created and shuffled. This is the initial shuffle. Then a server seed is randomly generated.
The hash of both of these are shown to you before you play. You can then supply a client seed, a default one is randomly generated in your browser or you can enter any text you like.
When you bet the client seed is combined with the server seed and the deck is shuffled again with the Mersenne Twister algorithm.
The has of the final deck is shown to you as you play and at the end of the hand the initial deck and server seed are shown to you.
You can use the provided tools to verify everything, Javascript code is provided.
Dice is done in same way except there's no deck or second shuffle. Just your client seed and server seed are used to pick a random number and you can verify it after the roll when the server seed is revealed.
A new server seed is generated every hand/roll.