You have probably found it when you see something that looks something like https://en.wikipedia.org/wiki/Terminal_emulator#/media/File:Xterm.png.
I will sometimes use the follwoing to illustrate it
┌─────────────────────────────┐
│[th@computer]$ │
└─────────────────────────────┘
You can execute commands by typing the name of a program.
Take the progam with the name date for example.
Type date and press enter.
┌─────────────────────────────┐
│[th@computer]$ date │
└─────────────────────────────┘
It shows you a the current date like so in the next line:
┌─────────────────────────────┐
│Fr 5. Dez 14:35:43 CET 2025 │
└─────────────────────────────┘
So what will be displayed on your shell looks something like this:
┌─────────────────────────────┐
│[th@computer]$ date │
│Fr 5. Dez 14:35:43 CET 2025 │
└─────────────────────────────┘
which is to a certain level available through the manual pages that are available for many progams.
They can be accessed via terminal with the program man,
so if you want read the manual for the program date you execute man date or
if you want read the manual for the program man you execute man man.
The program man takes you to somethung called "the alternative screen",
that is a place where you wont see the name of the program you typed in
and pressed enter after typing it to start the program with the typed name.
Usually you can leave the alternative screen by pressing the key with the letter "q" on it (q).
Now go ahead and execute man man.
Afterwards you may read man apropos which will help you searching for programs that
do something you are looking for.
Feel free read about using bash as a shell at ./programs/README.md.
Consider reading what "free software" is at https://www.fsf.org/about/what-is-free-software. A list of such software by categories of usage is at https://directory.fsf.org/wiki/Main_Page#Categories.
other sources: