Tempest Keep and Serpentshrine Cavern are both level 70, 25 man raid instances. It's essential that everyone wishing to join these raids reads a basic guide on the relevant instances before attending.
Please ensure you are well stocked with food, water, ammo, and plenty of potions before the raid begins.
We'll post more information about TK/SSC shortly, for now please refer to WowWiki's guides:
Tempest Keep:
http://www.wowwiki.com/Eye_(Tempest_Keep)
Serpentshrine Cavern:
http://www.wowwiki.com/Serpentshrine_Cavern