Openings

When we play chess openings as white and black should we focus on one opening, or try to learn multiple? 

For white, only one (your opening). For black, E4 or D4.

When you're starting chess I would recommend just starting on one opening and then moving onto multiple once you've figured out that opening move onto others

generally you want to stick to one and learn the type of position that comes from that opening really well instead of having to learn multiple openings and not knowing them as well. Should helps the rating and learning the opening in general

While I have favorites that I specialize in, it helps to have a familiarity with many as things can and will transpose to different lines.

You should create a general understanding of most openings but at your level the opening isnt too important and you should focus on tactics, defense, middlegame, etc.

@GunnaBeWannaBe After a level, you should also probably prepare for 1. C4, and at the master level 1. b3 and 1.g3

Although who am I to talk, I'm only 900

Obviously, but you are winning right away as black then.

Generally this should be learnt before master level

@Hikaru I respect your opinion

Play simple openings like the french, scotch game, or italian game. I have had a lot of success. Play the french against everything. If they play d4, then c4, do Nf3. Italian and scotch are similar, and have simple ideas. You also have to learn how to play against the pirc, caro-cann, modern, and owens defence to be completely safe. I am 1400.

When playing black, you need to prepare for the most common opening like the knight moves, e4, d4, e3, d3, and maybe g3. you can generally defend against the others with solid play or a solid system response like the kings indian setup. But, I am a 1300 at most so I don't go the greatest advice.