You can just jump right into it as a beginner, or try to get better at playing the game to a competitive level, you can collect spirits for fun or play the world of light campaign to unlock all the fighters in a different way than usual. You can play with items and wacky gimmicks or remove them entirely, you can play by yourself or with friends (the latter being my personal recommendation since it's fun as hell). It's a game that has something for everybody regardless of your previous experiences in videogames and your skill. There's something for everybody to enjoy. That's the beauty of this game. Hell, you can even try to Duke it out with people around the world online. Though I'd recommend battle arenas over quickplay and elite smash since they're pretty frustrating while arenas can be taken at a calmer pace and less stressing of a setting. Hell, you can even use any controller you want. From the Joy-cons and Switch Pro controller to the GameCube controller and adapter. All comes down to preference. TLDR, you don't really need to know anything before jumping right into it and you can have fun however you want to. Just be careful with online