Copy this list to your in-game notepad for convenient reference.
Key - NPC name: Damage Type it uses (Damage to use against it)
- Angel Kinetic/Explosive (Explosive)
- Amarr Navy EM/Thermal (Thermal)
- Blood Raiders EM/Thermal (EM)
- Caldari Kinetic/Thermal (Thermal / Kinetic for Temuras)
- Concord EM/All Dmg Types (Thermal)
- Gallente Kinetic/Thermal (Thermal)
- Guristas Kinetic/Thermal (Kinetic)
- Khanid EM/Thermal (Thermal)
- Minmatar Fleet Thermal/Exp (Thermal / Exp for Darkanas)
- Mercenary M/Thermal/Kinetic (Thermal)
- Mordus Kinetic/Thermal (Kinetic)
- Odamian Kinetic/Thermal
- Drones - all Dmg types (EM)
- Rogue Pirate EM/Explosive/Kinetic
- Sansha EM/Thermal (EM)
- Serpentis Kinetic/Thermal (Thermal)
- Zazzmatazz All Dmg types (Thermal)
You should choose the right type of ammo and resistance fittings for your shield or armour for the target you're against. It can be a +50% damage boost, or more, and equivalent reduction for damage taken.
Who you're fighting?
In the Mission journal, there's a little logo - which is pretty hard to identify - that tells you the type of NPC you'll come up against. Click it. That way you can prepare before leaving Station.
Tanking in Eve is similar to Warcraft. You install fittings on your ship which boost your resistance to the damage types in Eve: explosive, thermal, kinetic and electromagnetic. If your ship has 50% resistance to explosive, it literally cuts your damage received in half.
Resistance is generally a superior way to absorb damage than increasing your hit points. Items like '200mm armour plating' just give you extra hit points, whereas 'Armor EM Hardener' boosts your resistance to EM damage on armour and 'Photon Scattering Field' does the same for shields. Resistance fittings consume capacitor, though, so you'll need a higher level of power-related skills and fittings to make up for it, such as a Cap Recharger.
PvE in Eve is firstly about tanking. It's about soaking up enemy damage, and repairing the damage that does hit you, in a sustainable way so you have time to kill the targets.
Each race's ships have a bias to either shield or armour tanking, often with specific bonuses to the effectiveness of one type over another.
You should read more about tanking and skill yourself for it as appropriate.
Read this guide for much more detail and specifics.