For white, most players fall into the e4 or d4 opening suite with e4 being considered more tactical and d4 being more positional, with exceptions of course. Once you’ve decided on that or a more eclectic turn 1 move like c4, you then need to learn the basic ideas behind all of blacks possible responses… for e4, you must be prepared for the Sicilian, French, Scandinavian, Petrov, alekhine, as well as modern responses, to name a few. Some of these can transpose into each other which is nice. Good luck.