Impa tells you about them when you reach the village.
They can be done in any order, but the easiest is: Ruta, Rudania, Medoh, Naboris. Lanayru has Vah Ruta, Hebra has Vah Medoh, Death Mountain has Vah Rudania, and Gerudo has Vah Naboris.
The beasts are located in Lanayru, Hebra, Death Mountain, and Gerudo. To take control over these, Link must go to 1 of the four regions that their in. Link has to go inside and activate the terminals, then fight a Guardian. The Divine Beasts are ancient creatures controlled by Ganon. Warning: This page contains spoilers for The Legend of Zelda: Breath of The Wild