Study

There are multiple "from the ground up" type courses available on the market that teach you what you need to know in a structured way. There is also plenty of free content on YouTube. Just make sure you're focusing on content from players you know are beating the games as there is also some questionable advice from players who likely don't beat the games and just make money making content.

As a beginner/intermediate player I would focus a lot of attention on studying preflop spots as it's the one street you play every hand. Whether it's looking at charts or drilling spots, it depends what works best for you. Preflop is not the most interesting but it's foundational for range construction, and preflop errors tend to compound on later streets.

I honestly wouldn't be spending much time with solvers until you have a couple years of experience and are looking to move up beyond micro stakes.

ICM is important in MTTs, so you'll want to study the basics at some point so you make the proper adjustments late in tournaments. If you are going to use any solvers early on in your journey, I would recommend focusing on preflop ICM stuff.

If you make friends with someone who is beating the games you are playing they can help teach you heuristics and exploits that work in your games. For example a lot of spots can be simplified to small range bets with little EV loss (especially if opponents are over folding), and those types of simplifications make the game easier to learn.

Anyway good luck and have fun! I'm not sure what your goals are, but don't get discouraged if your results aren't great at first. Games are tougher these days, and I think it's best to think of poker as a (potentially profitable) hobby, especially when you're starting out.

Greatwhitefish, good info thanks for that.