Today, most consumers will think of Operating Systems as the Graphical User Interface (GUI) most commonly called either Windows 7/8/10, Apple OS 10 (El Capitan/Sierra), or one of several popular Linux distributions in 2016 are Mint; Debian; Ubuntu; openSUSE; Fedora; CentOS; PCLinuxOS; Slackware; PuppyLinux; and FreeBSD (unix-like).*
Yet, at times, it will be good to know how to use the command line OS commands (still used from back in the DOS/UNIX years) if you wish to tweak the operating system as a system admin, want to run scripts or batch files quicker than utilizing the GUI application. I will list several commands that helpful to know and their Windows/Linux equivalents (this will also work in the Apple OS terminal utility).
Depending on which you use, the place where the cursor starts off is called the Prompt and in DOS it may look like a letter follwed by a colon and then a back slash (for example, C:\) while in Linux it is absent of a letter and has other information and ends in a dollar sign (for example, me@linuxbox:~ $).
I have listed several sites that give comparison commands for DOS and Linux, what they are used for and do similar tasks (although remember that in linux, it matters if something is capitalized or not and will effect the way it runs or lack of running).
Learning how do do the more basic commands is a good start to learning how to run and use scripts. Try some basic things like showing your network connections by using either ifconfig /all in DOS or ifconfig in linux. learning to do a ping command which uses the word ping and an ip address like 188.8.131.52 which is one of several address to reach Google.com. See what it shows you.
* = here is a website for noting the popularity of linux distributions. It is a good place to check out what kinds are there and you may find several that may draw your interests to check out.