Melee is pretty complicated, but don't let that intimidate you. Everyone has to start somewhere. If you haven't already, make sure you're practicing your tech skill and movement. The faster you get down fundamental tech skill, the sooner you can start focusing on your actual gameplay decisions. Once you have a decent grasp on the basic movement techniques (short hop, fast fall, L-cancel, dash dance, wavedash, waveland), I recommend watching high level matches of Marth/Pikachu players and just try to implement the same options they are using. Even if you can only replicate one small thing at a time, that's progress. Maybe you notice a Marth player doing dtilt, dash back a lot. Load up 20xx, practice that until you can do it consistently, then try it in matches to see when it's good and when it isn't (referring to match footage is also great for speeding up this process).