Well, you gotta learn those combos. Go on FG (best place to find sandbags) or training mode and try them.
If you want to progress, you should go to the main sections of your mains on the site. Your mains are apparently
Lucina and
Roy, so click their names to go to their section. You can find a lot of tips and tricks to help yourself progressing.
Also, go on
Smash Ladder, you'll learn faster there. You basically play with rules close to those in tournaments, with different stages and all that stuff. If you're lucky, you could even find someone who wants to play with custom moves (pretty rare to find). It's great if you want to progress.
Those are my basic tips to progress. I'm not really that good myself (I'm a lot like Polnareff in JoJo when I play). So, stand proud and go train yourself.
Luggy giving tips instead of memes, a rare moment indeed.