How old are you and how long have you been playing? That matters when deciding how to attack learning from the ground up.
For me, I'm 34 and have only been playing on and off for a few years...mostly off due to life. In the past couple of months I've started taking things really seriously though and am preparing to start both USCF and FIDE tournament play. I do have a provisional USCF rating after two games played already, actually.
Anyway, my road was and is tough because I started in my 30's. I learned how the pieces move at about age 4 but that's it. I didn't even know about en passant. So, coming from basically a 200-300 elo on up was filled with so many horrible blunders, mistakes, and wins thrown away that I think I'm well prepared for the next set of horrible blunders, mistakes, and wins thrown away lol. That's what chess is about - learning from these experiences.
Do yourself this massive favor: Do tons of both timed and untimed tactics on ChessTempo. Tons. That is, by far, the best thing you can do right now to improve in live chess. You need to start seeing patterns and combinations, and developing the ability to see what the board would look like after a couple of exchanges. This is all tactical. Other than this? Play both blitz and long games (legitimately long games) and analyze all of them extensively. Extensively. Play a lot of games, too. Like...a lot of games. Just keep going over them, seeing where you went wrong, applying that in the next game, etc. Tactical work, playing games and reviewing them to this extent, studying endgames, and learning about different pawn structures and ...I mean within just a few weeks of this you'll improve greatly.
Despite what some may tell you on
Chess.com, you need to play blitz and long games, though. Don't avoid blitz. You're used to no clock and you need to get experience in playing during time trouble. Blitz will aid this and your tactical ability tremendously. The key is to make sure that you continue to enjoy and play long games, too but review both the blitz and classical extensively. Don't slack off on this as this is where you'll make most of your progress.
Lichess has done a great job of integrating the games database and openings book into the analysis engine here. You want to review master class + games that match the positions you're getting early in your games. Review the master games as you would your own, paying attention to every move's inaccuracies and mistakes. Before you know it, a lot of what seems very complex to you now will just be intuitively known.
That's just my opinion though but ...it's based off of listening to the advice of many titled players. I just did what they told me to do and it's working, basically. You have to love the game, though. If you don't love studying and playing chess, you'll never do enough of either to improve. Chess improvement isn't really a part time thing. If you want to legitimately get good, you have to put a ton of time and energy into it. You're going to lose a LOT before you start winning.