Starclan is the heavan-like sanctuary that Warrior cats go to when they die, if they were... not totally evil. Almost all ancient cats that died in the past went to Starclan, with Tigerstar, Darkstripe, Brokenstar, and Hawkfrost as exceptions, cuz they ARE totally evil.
Starclan cats "live" on Starclans hunting grounds, which is forest, but its sorta.... starry, like the cats.
cuz they're dead.
Bluestar and Spottedleaf died, now they're in Starclan.