What is a good beginner opening for black?

There are plenty of good openings to try but playing classically and fighting for the center are good starts. What openings have you played so far? What openings do you struggle to play against? 

U can plA 2-knight's defense if U R N aggressive player.

Well first it’s best to know the opening principles well, so whenever you get out of known opening positions you have concepts to work from. So after 1. E4 d5 2. E5- what do you think would be a good move?

Against d4, you can play many responses, but I suggest either d5 or Nf6. Try to attack the center early on.

I wouldn't recommend scandinavian against e4, of course it's an opening you can play, but an opening where you put the Queen in early. you can play e5 against e4. this is good for beginners. as your level increases you can learn openings like french caro-cann or sicilian.

Against d4 you can make a game like this:

your level is low yet, you just need to know the opening principles

Just keep it simple: Against e4, play e5 or d5, and against d4, play d5. Going for a semi-closed or a hypermodern opening as a beginner is much harder than fighting for the centre with pawns.

Other than that, you should just play principled: Adhere to the basic opening principles of putting pieces and pawns into the centre, developing all your pieces, not making too many pawn moves, not moving the queen out too early, getting king safety (Castling) and not moving the same piece too many times.

If you're really, really a beginner: mirror the moves white is making. Pawn for pawn, knight for knight, bishop for bishop, castling for castling etc. Do that for the first 4-5 moves. Thereafter, exercise your own judgement.

If I were you, I would play more daily games.  This way, you get to  spend time learning the openings and the concepts thereof.