You can do a lot using just commands on Linux. Through the Terminal, you can type the command that you want and perfume many actions and diagnostics. Depending on the distro you are using, you will have a different shell pre-installed (bash, dash, etc.). They can have small differences, but for the majority of command, they will work the same.
You can also change the shell if you like. Here you can see a Linux commands cheat sheet with the main commands and what they do.