Following info comes from Mega 3.
Here's a shot of the Magic Circle. The Magic Circle is what causes the monster to appear. A being, typically Lady Blue will bring a being's DNA over to the circle and place it inside and then she'll recite a spell which will cause the creation of the monster.
Here's Powerdriller.  
Here's a shot of the Black Ranger fighting Powerdriller.
Powerdriller was defeated by the Spiral Saber's Slash Attack. Hyprus is what causes the monsters to grow in Megaranger. When he's summoned, he can fade in and then he'll go over to the monster and he'll bite on them in order to inject a virus into them and the virus is what enlarges them. Here's a shot of Hyprus by Powerdriller as he's biting it.
Here's Giant Powerdriller.
Here's a shot of the Astro Megazord with its Shield.
Here's a shot of the Astro Megazord with its Saber.
Here's a shot of the Astro Megazord powering up its Saber and then the Megazord goes in to attack Powerdriller with its yellowish powered-up Saber, this attack is what destroys Powerdriller.