Meh.. do only I see lack of info from the ED side? Putting aside above (great) advice I see frustrated CMDR that got his ship and went for some action and got his stern handed to him on a silver plate. And now he sits, infuriated, not knowing what hit him.
To sum up above:
- not every combat situation is the same. We have something like gradation in difficulty. Nav beacon bounty hunting is the easiest since NPCs there are the weakest. Then Resource Extraction Sites, next combat zones but those require engineering since opponents use them on regular basis. And engineering adds so much to performance that non-engineered ship has little chance vs engineered one. Last part is Thagroid hunting which require specific loadout to be successful.
- difficulty rise with your combat rank and NPC combat rank is main indicator how difficult your opponent will be. Not the ship type he's using. Dangerous Hauleer may sound silly but don't be surprised if he mops the floor with your combat ASP.
- you need to learn a bit about weapons, shields and armor. As said earlier - energy weapons are effective against shields but are not that great on hull. Projectiles are effective on hull but not so much on shields. Turrets are weaker than gimballed and fixed are better than gimballed (rough and basic difference). Optimally you want some enegry for shield stripping and then projectile for hull. Call it starter set and work from there, fitting to your needs.
- last but not least - ships. Some ships are excellent explorers, some are terrific cargo runners, other are best at combat. Facing such combat oriented ship may be frustrating at start as you get the tough nut to crack. Read about ship types, sizes, their general role and pick your targets wisely.
ED isn't easy game. More times it will kick you in the face, add under the belt hit and spit on your miserable failure. You can try to beat it head on (and rage quit after failing), be persistent and slowly try to learn and overcome difficulties (judging from your post, not the option here) or stay on forums and ask multiple questions about combat, loadouts, tactics, etc. Many knowledgable people here.