One of the most frustrating things for some people can be learning the path to a file or folder. It actually intmidates some people to just give up. So if you're using Steam, and you want to use some of the awesome Liveries and scenery addons here is the path to your "Community" folder where you can place the items you downloaded after you unzip them.
C:\Users\Username\AppData\Roaming\Microsoft Flight Simulator\Packages\Community
"Username" is your username you use to log onto your computer. So you can copy that path above and replace "Username" with your computer username and paste it in the address bar of your file explorer window and hit enter, and you're where you need to be.