I have never played classical chess in my life. I used to play a lot of online blitz and was around 2100 but I'd be a lot worse now I don't play regularly.
There are lots of resources to improve your chess online. Lichess is my favourite site.
https://lichess.org/practice
Teaches you the basics of tactics.
https://lichess.org/training/
Tactical puzzles generated from real games.
For learning strategy you have to play slow games and analyse them after with an engine. Again you can do this on lichess, against other players or a chess engine with various difficulty settings. You don't need an account.
If you have the time then there are a ton of good chess youtubers who you will benefit from watching.
https://www.youtube.com/channel/UC6hOVYvNn79Sl1Fc1vx2mYA/playlists
John Bartholomew's climbing the rating ladder and tactics training series are super instructive.
ChessNetwork and GingerGM also have a lot of good videos. Remember to stick to longer games. Watching someone play a single 30 minute game is much more instructive than watching them play 30 bullet games.