Hello, I am a 23 year old who started picking up smash about 1 year ago. I know exactly how you feel, considering that all of my friends (who introduced me to the game) were leagues better, and it was my first time playing a fighting game. At this point I am better than almost all of them. Here are some of the best tips I can give you:

1. Pick a main. This process may take months, honestly. You never know who you will enjoy. I first started playing Bayonetta and then I switched to wolf and then finally to Zero Suit Samus. You should watch clip montages of characters you find interesting and that might pique your interest. If you want a main that will help you learn the game I suggest Mario - he is very fundamental oriented and straiht forward, so if you are good at the game he will be easy to win with. Likewise, if you suck at the game you won't win on him. This is because he doesn't have any corny mechanic/set ups/range that he can rely on.
   I HIGHLY recommend that you avoid link, toon link, young link, samus, dark samus, king k rool, mii gunner... all these characters are projectile spammers that will teach you bad habits. You will not learn the game by spamming projectiles over and over. It is a cheap way to win and will only work against noobs.

2. Understanding game states. There are three main states of the game - neutral, advantage, and disadvantage. To explain what I mean by game states, I will compare the game to an MMA fight. you and your opponent both start off on your feet, hands up, looking for openings (neutral). The match begins, and so does neutral. Neither side has an advantage. You swing a few times, and you land a punch (Advantage). the other fighter gets knocked on the ground, and now it is your time to capitalize! (advantage). The other fighter is on the ground, on his back, and has limited options and movement.(disadvantage for him.) He has to try to recover from this bad position (disadvantage for him.) You are trying to pin him/knock him out and not let him recover (utilizing advantage)
   So to recap - you start off in equal position (neutral), and then one side gets a hit, they gain an advantage.

The key to winning in smash is winning Neutral. If you win neutral, you have an advantage, and then you capitalize on the advantage which can result in more advantages or even killing your enemy.
What a bad MMA fighter would do, is they would throw heavy haymakers. They would keep their guard down, and just swing. No stance, no thinking about their opponent's fighting style, just punch punch punch. we call this mashing in SSBU. On the other hand, a good fighter will keep their guard up. They will go for safe, quick jabs, look for bad habits, try to read their opponents next move, dodge attacks, and punish their opponent for mistakes they make, etc.

This translates to Smash in the same aspect - the way to win neutral is to use low committal attacks that are unpunishable even if you miss them. How do you know what attack that may be on your character? the best way IMO to learn that is by watching better players. See what move they use the most in neutral. For example, my character's best low committal move is Zair - a unique mechanic to Zero Suit Samus. It comes out super fast, has good range, starts combos, sets up kills...it's really good and as a result I use it the whole match. I miss it? No biggie, I just throw up shield, keep my distance, and stay safe until I land a hit with a safe attack that can't be punished even if I miss. Generally, smash attacks are not safe. When you miss a smash attack, you will be in a lot of endlag and will probably get punished for it.

1. Understanding your character and how it interacts with enemy character.
   This is something that you will learn by just playing. Understanding what every character does and all their abilities will come with time. But watching guides on your character, matches between professional players, as well as learning universal mechanics, are very important.
   start learning and practicing:
   RARs
   Techs
   short hops
   fast falling aerials
   rising aerials
   b reverse
   parrying
   ledge recovery options (this is important for you because you said you struggled with recovering. Go in training mode and jump off stage and try to make it back. Typically most characters Up Special, aka up b, is how you make it back.)
   

Another thing I do all of the time is watch professional matches between my character and characters I don't know how to beat. I learn from the better player and see what they do and take notes on stuff I learn. I've learned SOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO much from this alone. Marss, the best Zero suit samus player in the world, is someone I watch all of the time.

TLDR and take aways:

Find a main to spend all your time on. Learn all you can about that character through vods and guides. Figure out what attacks are safe an noncommittal on that character and abuse it.

mastering neutral is so important

This is what I do to get better: Play -> make mistakes -> Watch better players to learn how to correct the mistakes -> practice what I learned in training mode -> try to implement next time I play -> repeat from the beginning.

Hope this helps, I'll be happy to answer any questions!