I know the openings, but when to use them?

edit: This is not my acount, its my boyfriends, I forgot to check which one was loged in when posted. Im rated 1200-1300 somewhere

correct me if I am wrong, but with internet chess I do believe you only need three openings as white.

Ofcourse you can become the life of the party by remising about the opening used by Karpov in his 1978 world championship game (it was the queens gambit declined, since you were obviously wondering), but for any other scenario you only need three:

1: an aggressive opening to play against a weaker opponent

2: a medium type of opening to play against a player of equals strength 

3: a defensive opening to play against a stronger opponent

So I turn to the chess.com community to ask, which three openings should I choose, and why? If you could, please list three and a small comment as to why that opening is a good choice. 

It's quite wrong to play aggressively against a weaker opponent. You will beat him by class only without much risk in any reasonable opening.

For the same reason it's even more wrong to play defensively against a stronger opponent.

Play against the pieces, not against the opponent. And there is no need for openings at your current level.

The right openings for you vary upon style. There is no "these are the best 3 openings" you can use. It's about how you feel and understand the position.

I am in accordance with IM pfren. With white, you should not be too defensive, even against players much higher rated. Be a little ambitous, keep to your ideas like controlling the centre. If you are playing a stronger player, they will still probably beat you if you are defensive because they will eventually grind you down. I was always taught, play for a win, because you find the best moves that way. if you are playing for a draw, you in general will play mediocre moves. The person in front of you may be way worse than you expected, in which case you could have won. Or in my case, I had a 1000 rating and was beating numerous 1600's because i was playing for the win. I HAD NOTHING TO LOSE as the lower rated player. They played too aggresively, and almost all of them dropped an exchange or piece. i played my best chess, and played agaisnt the board. My rating is now in the 1600's itself. I did not play defensively, trying to work a draw, i played my best untill, i either won, or they simply outplayed me. I did draw in some games, but this was after a struggle from both sides giving it their all. 

I believe all people should look at it this way. Ofc this does not mean make risky moves that might lead to checkmate, i mean play positional chess that maintain an advantage, and overall just making logical decisions to you, not ones that you think it gives me a better chance to draw. Such as white playing exchange french, this is not nearly drawish as everyone seems to think.  

@ Nerwal I see your point, but on the other hand when you play aggressively and know your stuff the weaker player is more likely to be outplayed and lose faster

If your opponent is much weaker, you can win against him without taking any risks. And a win is one point, no matter if this is in seventeen moves, or seventy.

That's wrong. You should play a defensive opening against a lower rated player.

First off, it's not that easy to know everything in an opening. Secondly, there is no prize for winning quickly, winning safely is as important if not more. Then, in a sharp position the value of each move gets much higher. A single slip can have dire consequences, even in overwhelming positions. In addition, the psychology of the match-up ("I can't afford to lose to this guy") doesn't help.

The idea of playing normally is based on statistics : on average your move quality is higher, so over a batch of moves it will tell sooner or later. Time and again I have seen lower rated players playing decently some phase and then collapsing for no discernible reasons.

Play the position on the board.  

At your level, you dont need to learn openings, just opening principles.

hey, I edited the question. The same probably holds, but im rated 1200-1300 at this site, this is not my acount, just forgot to check which one was loged on :) 

another question, if Im suposed to not play defencive against stronger players, are there any reason to play defencive at all? 

If you dont know how to play, this is another example of why you shouldnt be asking about what openings to play.

The question was if you are not suposed to play defencive against stronger players does that mean you should play defencive against Weaker players, and if not when should you do so?

You play the position on the board.  You look for the best move, not the best defensive move, not the best agressive move.

"Every now and then someone advances the idea that one may gain success in chess by using shortcuts. 'Chess is 99% tactics' - proclaims one expert, suggesting that strategic understanding is overrated; 'Improvement in chess is all about opening knowledge' - declares another. A third self-appointed authority asserts that a thorough knowledge of endings is the key to becoming a master; while his expert-friend is puzzled by the mere thought that a player can achieve anything at all without championing pawn structures.

To me, such statements seem futile. You can't hope to gain mastery of any subject by specializing in only parts of it. A complete player must master a complete game ..." - FM Amatzia Avni (2008)

"... For players with very limited experience, I recommend using openings in which the play can be clarified at an early stage, often with a degree of simplification. ... teachers all over the world suggest that inexperienced players begin with 1 e4. ..." - IM John Watson in a section of his 2010 book, Mastering the Chess Openings Vol. 4

He went on to suggest possibilities for how inexperienced players might react to the Sicilian, French, etc., as well as possibilities for how inexperienced players might react as Black to 1 e4 and 1 d4. Pete Tamburro wrote his 2014 book, Openings for Amateurs, in a similar sort of spirit, saying that it was for "club players." ("... the outside boundaries for the group will be defined here as between 1100 and 1900, or people who want to be there.")

http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html

"... Hansen then follows this with a very thorough discussion of his three-step approach to preparation for a specific opponent:

1. Getting an overview of the opponent's opening repertoire;

2. Narrowing down the possible choices to a few options;

3. Preparing the specific line. ..." - Steve Goldberg in a review of the 2008 book, How Chess Games are Won and Lost by GM Lars Bo Hansen.

What I meant with ''faster'' is that you are more likely to beat them in sharp (agressive) positions, especially if you know your stuff. Because what you say, the cost of a slip up is higher and the weaker player is way more likely to slip up. You don't need to know everything, knowing thematic ideas will prove your superiority. And if a weaker player beats you in an agressive opening you know well (I said ''know your stuff'', which is interchangeable) then that player probably wasn't weaker than you after all.

Even if the weaker player survives the complications you can still win in an endgame, or 70 moves as Pfren said (even though in a tournament that can actually affect you in later games) without playing a dull game in which it's harder for the weaker player to slip up.

You say ''playing normally'' but I don't really understand that because agressive openings are considered normal (not extraordinary) openings too (Dragon, KID for example).  

Playing the board is not necessarily a good idea. Against stronger opponents, play sharper (especially in the opening), as this puts them under pressure and either of you can blunder and lose. You're more likely to than them, but playing passively will just result in you being ground down. My results against stronger opponents are suspiciously good.

Also, play to your style. Don't necessarily play the 'best' move if it is not in your style. On the flipside, if your opponent is a tactical genius, try to get to an endgame or at least a solid position. If he is a good endgame player, complicate matters before you get to an endgame.

Against weaker opponents and those around your strength, play your normal style. Otherwise you are out of your comfort zone (and possibly in theirs).

Well playing in the style you feel comfortable with/your style is probably the easiest solution and a good point to make. I can't recall that one mentioned before in this thread, surprisingly. I always play the same openings though. I trust my knowledge no matter against who.