Let’s open with chess openings.
Chess openings are the first several moves mapped out. The actual number of moves differs from opening to opening. These moves are referred to as “theory”. Theory does change but changes are often quite deep beyond the 15 move mark. The Najdorf Sicilian is now at move 30 and a slight misstep even at that point can be disastrous to someone else familiar with why the newer moves have replaced the older ones. In general though, knowing the first 10 moves of most common lines of each opening is important, but also you must know which openings you actually have to know those first ten moves of. Although when a reporter asked Fischer for a chess lesson Fischer said to go through every line and every footnote of the Modern Chess Openings, and for a second lesson to do it again (and thus know every single one as deep as common theory was in the 1970’s).
First the easy part. As black you need a defense against 1.e4 and 1.d4. Now 1.c4 and 1.Nf3 are also common, but it is very rare that they won’t end up transposing back into 1.d4 lines. Against bizzare stuffs like 1.b4 just play close to the vest in a Philidor-like position (…e5, …d6…Be6…Be7…Nf6…Nd7) and you won’t have to worry about a silly trick that he is trying to push for. It is not as important which particular defense you choose, but it ought to be a fairly normal one, and I’d advise against the Sicilian and gambit lines– Gambits are best for white.
The exception to this one 1.e4 and 1.d4 defense is that if you choose the Nimzo-indian, you also have to have one for 3.Nf3 like the Queen’s indian or Bogo-Indian.
For white you have to decide if you want on the 1.e4 or 1.d4 train. Doing both is a lot of work, so not recommended.
For 1.e4 you need to learn:
- …e5, 1…e6, 1…c5,1…d6/g6, ,1…d5,1…c6 (1…d6 and 1…g6 tend to transpose into each other).
That’s double e-pawn, French, Sicilian, pirc-modern,Scandinavian, caro-kann
You need to know how to handle each of those of black’s defenses.
For 1.d4 you need to learn
1…d5, 1…Nf6, 1…c5
Double dpawn, indian lines, benoni
Now these tend to split more down the line than move 1 ie queen’s gambit accepted or declined, slav, semi-slav, king’s indian, gruenfeld, nimzo-indian
There are tons are wonderful videos for the openings you choose to look into on youtube, most are far better than I can do, but I just want to tell you what you need to know.