Tutorial, I can't remember, but I do remember some pointers:
- Termux first needs the phone to be rooted to properly interact with anything outside of its $HOME, including Android's user's internal storage and SD card
- Iirc Termux lists useful packages in its default text, including the one for being able to interact with root
- Termux is a Linux distro heavily adapted to work as an Android program, but that makes commands familiar; if you used Debian, Ubuntu, Mint, etc., commands follow the same structure as apt's, but using pkg instead