Followed opening principles, still lost, unsure what I did wrong.

Speaking of resigning, I think White resigned way too early.  You're down a minor piece, but you are not under any immediate threat.  Your pawns are solid, you have space, your development is complete.  

Black has ...Nf3+, which would be a painful thorn in your side, but I don't see a quick follow-up.   Let him prove me wrong.  He hasn't really attacked all game, play a little longer to see if he knows how.

Let's see whether Black knows how to break through on the kingside.  (Sacrificing a knight on h4 should do the trick, but then material is almost even, so you still have a fighting chance.)  

Good point nartreb! In fact, I would go a bit farther and say that at the 1000 level you should almost never resign. There are some exceptions, of course, but you should get in the habit of fighting every game until the end and never quit trying. Your opponent is just as capable of blundering as you are. Chess is a fight

I think 11.Qd3 is playable if you play Nxf7 next.  I think 12.Bf4?? throws away the win though.  It doesn't expose Black's king.

Basically, you forgot to attack him when his development was bad and he's made lots of weakening moves. Instead, you allowed him to take your knight. You also wasted moves with things like a4, which doesn't follow opening principles. I would have considered 6. e5, to start an attack, getting your pieces in behind the e pawn. Also your white squared bishop was probably better on d3 than c4 since he weakened his g6 square so much with h6. Just crying out to be attacked. I don't know about f3 .... a piece sacrifice might have worked. Your opponent played so badly that the direct approach was correct.

Agree completely with shammaarb. There is no point in nitpicking the opening, it was fine. Every move had at least some reasonable purpose, and after 10 moves, White was way ahead in development, controlled more of the center, and had the safer king. What more do you want? 

I do agree with the above. I think white is won after black's 9 ...b6. I think white must play 10. f4, with the intention of possibly pushing that pawn all the way if allowed. I don't like the N on e5 because it prevents the natural d5, attacking the uncastled king's position. But f2-f4 makes sense of the Ne5 and I'm sure must be winning. I would expect to beat anyone less that 300 elo points stronger than me from there.

I'm sure Kingside castling was correct. There's simply no need to go q-side. Black is a shambles.

My guess would be that your opponent's strategy was mostly to wait for you to blunder. It may be annoying that that plan worked in this game, but getting your pieces active is part of the road to better chess. With practice, you will get better at avoiding blunders and taking advantage of an opponent who mostly just advances pawns. I am not sure what you have in mind by "kamikaze", but there seems to be agreement that some sort of pawn advance would have been appropriate in order to work on exposing the black king's position.

As others pointed out, this particular game was lost due to a blunder (losing the knight), and games at your rating level, and at mine rating level for that matter, are usually won or lost by blunders.

I have been playing chess for 1.5 years and i struggle to stay above 1100 in blitz and 1300 in rapid and i have put in lots of time & effort to improve, so there is nothing wrong with you, chess is damn hard, especially if you start play at a later age.

What helped me the most is watching tons of videos on youtube regarding openings, middle game, endings, commentary on master games etc and do a few lessons & tactical exercises on this site to hammer the thought process and pattern recognition into my head.

I am still hoping that my opponent makes blunders, and if he don't, then i start to struggle finding a good plan and usually ending up blundering myself. The better you become, the finer mistakes of your opponents play will you be able to detect and take advantage of.

Your opponent played the Modern Defense. You, as a beginner, should continue to follow with the classical rules, but higher-rated players can choose Hypermodern opponents which don't follow these principles at all.

That opening doesn't have a name, but if it did, it'd be like... the retarded hippo defense.

the modern defense is e4 g6. He played an offbeat line afterward.

That's what I'd expect a new player who is going off an online database thing to say.

But I don't think anyone (experienced) would call this the modern defense. Just saying.

https://en.wikipedia.org/wiki/Modern_Defense

Yes, I know, I learned that when I was a beginner, just like you.

Whoa, that was harsh.

Here we go again. Nobody put Wikipedia in charge of opening terminology. This sort of issue has come up before. A similar discussion took place at:

https://www.chess.com/forum/view/chess-openings/sicilian-defense-closed-variation-3?page=2

(Whether or not the Closed Sicilian was defined by 1 e4 c5 2 Nc3.)

If I remember correctly, there was another argument over whether or not the Smith-Moira was defined by 1 e4 c5 2 d4.

https://www.chess.com/forum/view/general/why-is-the-smith-morra-called-a-gambit

I think that the main culprit is computer software that has somewhat simplified opening terminology, changing it from the way that it has been viewed by many. Computer sources are apt to simplify and approximate actual human usage because it is pretty hard for computers to duplicate it. Nobody is an appointed terminology authority, but titled players are more apt to have an idea about what helps to convey important chess concepts to each other. Since they are also the ones who do most of the chess writing, it seems to me that it might be sensible to try to be in tune with the way they use language.

It would have been the modern defense until it transposed into the Pirc, but they both played offbeat lines.

No reason to say what it “would have been” except that you seem to want to do so.