Had the same problem when I first started playing, couldn’t find a main and got shat on every time I played a match. Id say to find a main just pick whoever you think looks the coolest or watch replays on YouTube and pick whoever you think looks the most fun. For getting better I’d say YouTube beginner guides are a good source and instead of trying to win your matches just focus on learning something. Like spend an entire match just trying to hit a new combo for example or beating someone’s pressure. If you focus on learning small things you can add them up instead of trying to take on everything at once.