Why the shell

Composable tools and repeatable work.

What you gain

The shell lets you combine small programs into one job and repeat it exactly. Anything you can type, you can save as a script and run a thousand times.

It is often the only interface available on a server.
Bash is the common default; zsh and fish differ mostly in comfort features.

Reading a prompt

The prompt usually shows user, machine and current directory. A trailing dollar sign means an ordinary user and a hash means root, which is worth noticing before pressing enter.