Termux is basically a command-line Linux distribution that you can use on Android. You can download it here:
You can either download F-Droid and install it through that, or you can download the APK on the same page (the version of your choice). The information herein was tested on Termux 0.106, on Android 10 (but there are newer versions of both Termux and Android).
Here are some very helpful keyboard shortcuts (when you have such as a bluetooth keyboard connected to your Android device--which I highly recommend):
(Some important shortcuts to remember currently include ctrl+alt+down/up to switch between Termux instances, and ctrl+alt+c to create a new one. Also, ctrl+alt+r to rename a session, and ctrl+alt+right/left to open/close the sidebar, or drawer, and ctrl+alt+v to paste.)
The drawer is a sidebar that shows you all your sessions by number/name; you can click on a session to navigate to it.
To exit a session (a Termux instance), type exit.
Congratulations! Now you can multitask on Termux on Android!
You can also create a new session with a Termux widget (long press on the Termux icon in Android 10 to find the place where you can create the widget that lets you start new sessions).
I wrote this after finding these incorrect suggestions highly ranked on Google:
I also recommend checking out Ki if you're serious about using Termux to turn your Android tablet into a workstation: