I was a high schooler when I was learning to code. I had a laptop but only the breaks between classes to do it. So what I'd usually do was get up in the morning and learn something, then sporadically practice and experiment with it for small chunks of time. I'd usually start by adding comments for what I want to do so I don't lose track.

I don't know if this is applicable to actual computer science but worked for me for the programming part.

Apps like Enki also have helped me but not in a really transformative way.