Once per turn: You can pay 500 LP; during your Main Phase this turn, you can Normal Summon 1 "Vampire" monster, in addition to your Normal Summon/Set. (You can only gain this effect once per turn.) Each time your "Vampire" monster inflicts battle damage to your opponent: Gain the same amount of LP.
Gain Life Points equal to the damage inflicted by your “Vampire” monsters.
Need to pay 500 LP in order to activate the effect.
The additional Normal Summon/Set is only once per turn and it needs to be a “Vampire” monster.
“Call of the Mummy” is a very similar card that widens the range of monsters you can Summon and it has no cost.
Using a Vampire deck can quickly drain your LP, so using this card provides you with a way to recover lost LP and give you additional summons which are helpful in Vampire decks. Damage you deal to your opponent with Vampire monsters will recover you by an equal amount. Vampire Kingdom gives your Zombie monsters an additional 500 attack, which could help you deal more damage with Vampire monsters and therefore gain more LP.
You can also use this card as cost to revive Vampire Familiar or Vampire Retainer to get a search. Activate Vampire's Domain and pay the 500 LP cost for an additional tribute summon, and then send Vampire's Domain to the graveyard to revive Vampire Familiar and search a high-leveled Vampire monster. With the additional summon of Vampire's Domain you can summon the Vampire monster you searched with Vampire Familiar as tribute.