Depending upon the ethos of the priest or cleric in question, they may possess the ability to Turn or Control undead.     Turning undead forces those affected to flee at their standard movement rate for as many rounds as the turning character has levels.   If they are sentient, they need not flee, but cannot get within 10' of the turning priest or cleric that has successfully turned them.    As a standard rule, a successful turning attempt will affect all undead within a 10' radius of the turning cleric or holy warrior.  Control attempts can only be exerted within the 10' radius.    All undead within the radius are affected by the turning/controlling check, as are any undead that enter the turning/control radius.  In any case, the turning/controlling character rolls only one time.   For example, say that Rel-Thas the cleric is standing in a hallway when a pack of zombies and a ghast come falling through the ceiling.    He rips his holy symbol from beneath his tunic and summons his holy presence, resulting in his player making a Turning check.    Rel-Thas is a 5th level cleric in this example.    His player rolls a 1d20 and gets a 9.     Zombies are 2 hit die creatures, and are automatically turned, as Rel-Thas knew they would be.   The ghast, however, is a 5 hit die creature.  Rel-Thas needs to roll a 10 or better to turn 5 hit die creatures.   The result is that the zombies are hurled away from him, whereupon they shuffle and drag themselves away as fast as their rotten limbs can take them.  The ghast, however, only sneers and leaps upon Rel-Thas.

Note that any sentient undead with character levels, most notably the likes of Ghosts, Death Knights, Vampires, Liches and Greater Mummies, are turned/controlled based on their levels possessed.   Such undead creatures as Dracoliches and other phenomenally powerful undead have their own listing, and only the most powerful priests or clerics can even begin to hope to turn or control them.     Also note that any Dracolich that was a dragon of the 7th age category or better, or any undead of similar potency, is simply immune to any form of mortal turning or controlling.  They're just too powerful, and even a 30th level priest or cleric would stand no chance of subduing such titanicly potent foes no matter what they rolled.  Naturally, this is often discovered the hard way.    In any event, the turning/controlling cleric rolls one attempt and cross-references the number they roll on 1d20 with what is needed to turn a particular hit dice or type of undead they are facing. The hit dice run from left to right at the top with the numbers needed to turn them listed below.  Priest/Cleric level runs from top to bottom on the left side.

Some clerics and priests do not receive turning or controlling abilities.  Those types tend to have other powers rather than turning/controlling.   Paladins may Turn undead as a cleric 2 levels lower, gaining the ability at 3rd level.   Justifiers may Turn *or* Control undead, decided at 3rd level when the ability is gained. Once decided, this can never be changed.   Dark Paladins Control undead as a cleric 2 levels lower.    No classes beyond these gain this special ability.