It is a typed-command room living on the same device. Inside that room the phone pretends to be a small Linux computer. Many servers on the internet use Linux. That is why these skills transfer later.
Home is a folder
The ~ mark means “my home folder inside Termux.” It is not your photo album. Files you make with nano live in this inner house unless you share them on purpose.
pwd
Ask: where am I standing?
ls ~/learn
List the first programs, if you already made that folder.
Two filing cabinets
The Files app shows Downloads, Camera, and Documents. Termux has its own tree. termux-setup-storage builds a doorway between them. Until you use that doorway, a file in ~/learn will not appear next to your pictures.
That surprise is common. It is not data loss. It is two rooms.
A little deeper
Why the dark screen looks old
The typed command line is older than app icons. It lasted because it is precise. One line. One job. Servers still live here. Your phone is borrowing that dialect.
Package versus app
On the home screen you install apps. Inside Termux you install packages with pkg. Same idea, smaller room. Python is a package. Termux itself is an app.
Next step
One more Android room, for later: what a screen of an app is called. You can skim it now so the words are not new in Stage 5.