Offense
Offensive plasmids give you the ability to attack your enemies. "Electro Bolt" allows you to fire a bolt of electricity that damages and temporarily stuns your enemy. "Incinerate" allows you set an enemy on fire, and enemies can spread the fire to each other when in proximity. "Winter Blast" freezes enemies, allowing to you attack them without without taking damage. "Telekinesis" gives you the ability to pick up and throw objects at enemies and to deflect incoming explosives.
Defense
Defensive plasmids allow you to avoid taking damage by disrupting enemy attacks. "Cyclone Trap" throws enemies who spring the trap into the air, temporarily stunning them. "Decoy" creates a false image of you that enemies will attack instead, allowing you to reposition behind them. "Scout" gives you the ability to see what lies around corners so you can plan your attack accordingly. "Hypnotize" temporarily enchants an enemy to fight on your side, giving a you needed ally when fighting some of the game's tougher opponents.
Summon
Summoning plasmids allow you to summon creatures or robots to aid them in battle. "Insect Swarm" calls forth a swarm of bees that attacks all nearby enemies, and keeps them too distracted to attack. "Summon Eleanor" costs all of your EVE to use, but Eleanor deals lots of damage to enemies and stays with you for an extended period. "Security Command" summons a security bot to fight by your side, and lasts until destroyed.
Leveling Up Plasmids
You can level up each plasmid, with the exception of "Summon Eleanor," to give the plasmid more potency and additional effects. You will be able to unlock each of the available three levels as you progress along in the game. Upgrading requires you to find the higher versions of the plasmids, and most are found in either safes or EVE stores.