As several others have already stated, study from the CardsChat 30-day training course and absorb as much content on YouTube, Twitch, poker forums, and poker training sites as you can. I also like the idea of playing extremely tight--you may find it to be too tight, and then you can start loosening up little by little until you find a place you feel comfortable and is profitable in terms of acquiring chips.
Regarding what stakes you are going to play, it's totally up to you--a lot of people are recommending freerolls or even play chips, which is not a bad recommendation to start, but I feel (from personal experience) that you somewhat have to re-learn how to play in real money stakes compared to freerolls and play chip games; therefore, it's not a bad idea to play some super micros (approx. $3 buy-ins or less). However, the key here is bankroll management--professionals recommend that your bankroll (the money you are willing to lose) is 100x your average buy-in for SNGs and 300x your average buy-in (ABI) for MTTs (e.g., if you were to start with a $100 bankroll, you should abide by a $1 ABI for SNGs and a $0.30 ABI for MTTs). Most importantly, only play with money you are willing to lose, and do not jeopardize your financial situation. Once you start figuring out how to play and which stakes you can be profitable, your bankroll will compound upon itself.
Cheers, and good luck!