Amplify is a keyword ability.
It is a static ability that appears on some creature cards. As a spell with amplify resolves, its controller may reveal any number of creature card that share a creature type with them from their hand. If they do, the creature with amplify will enter the battlefield with a set number of +1/+1 counters on it for each card revealed.
Abraham is casting a Kilnmouth Dragon and has two Dragon cards in his hand. As Kilnmouth Dragon resolves, Abraham reveals both of the dragons in his hand. Because Kilnmouth Dragon has amplify 3, it will enter with 3 +1/+1 counters for each dragon, for a total of 6 +1/+1 counters.
- 702.37a. Amplify is a static ability. "Amplify N" means "As this object enters the battlefield, reveal any number of cards from your hand that share a creature type with it. This permanent enters the battlefield with N +1/+1 counters on it for each card revealed this way. You can't reveal this card or any other cards that are entering the battlefield at the same time as this card."
- 702.37b. If a creature has multiple instances of amplify, each one works separately.