There are a LOT of mostly free mobile apps out there, aimed at teaching you how to code (better).
I already went through some of them :
- Sololearn : it is great for beginners, with courses on HTML, CSS, JS and a lot of programming languages. But also on algorithms, regular expressions, data structures, design patterns and such. Add sandboxes and challenges to the mix and you get a great app.
- Enki : your daily routine to get better at coding (on a many topics).
- Codemurai : really great for beginners (JS and such) as soon as you get used to their economic model.
- Grasshopper : thanks google for teaching us JS from scratch.
There are probably tons of others but if you could recommend a few free android ones, that would be awesome. Not only for beginners but also to get better at coding (like Enki) and maybe explore new coding topics.