It reaches 15 metres around you and uses your Cleric levels. Your Paladin or Blackguard levels -2 are added too, whichever of the two is higher.
The turning check is 1d20 + your Charisma modifier. It sets the most powerful creature you can turn: from your turning level -4 on a total of 0 or less, up to your turning level +8 on 40 or more.
The pool of hit dice you can turn at once is 2d6 + your Charisma modifier + your turning levels, spent from the nearest creature outwards.
A creature with hit dice at most half your turning levels is destroyed. Anything else flees for 5 rounds (30 seconds).
Players are harder to turn: every 4 levels a player has add 1 to the hit dice you have to beat.
A player who is turned flees for 2 rounds (12 seconds) instead of 5.
Turn resistance and, for outsiders, spell resistance are added to the hit dice you have to beat. Planar turning halves the spell resistance part.
Domains widen what you can turn: Air, Earth, Fire or Water for elementals, Plant for vermin, Good or Evil for outsiders, Destruction for constructs, which take damage instead of being turned. The Sun domain adds 1d4+1 to the check and 1d6+1 to the pool.