Well, is this your VERY FIRST Smash Game, or have you played Smash before...?
Judging by "I literally have no idea how to play" I'm going to assume this is your first one. If that's the case, I would suggest just messing around with the game first before actually trying to learn it. You want to get a good feel of it and especially it's wide array of characters. You need to decide on who fits you best, who you like, or who you simply want to learn to be honest.
So really try out all of the characters, even if it seems like you won't have any interest in them. You might be surprised.
It's okay to like more than one, but I would suggest picking one to stick with for a while because it's gonna take a lot of work to get better with one character. It's especially true depending on how technical/hard that specific character is to master as well.
Once you know for sure who you want to start with, just try to find videos and guides on the character.
That should at least be a good start. The important thing is don't rush yourself, and to take one step at a time.