Termux is a free and open source Terminal Emulator for Android. After installing it, you will get a terminal box where you can install required tools and use them just like you do on a Unix machine.
This tools lets you educate yourself about GNU/Linux and programming (C, Python, Rust, ...) in a *real* environment even if you do not have access to a PC. And even if you have a PC, this tool will give you access to a Linux terminal (and all the man pages, curl commands and ssh sessions) wherever you have your phone / tablet.