Which linux...there are many, and some very different.
(I do not know if a "chrome"book is capable of running Linux or windows???)
Generally.... you download to your computer the iso file for the linux you want. Then you burn or write, (not copy), that iso file to a dvd or a usb stick. Once the iso is written to the dvd/stick it is then an install disk. Use that to install.
Just boot your chrome book on it. If it asks for a password on boot up- ignore it. Just let it go through.
Select "Try" instead of "Install". Let it boot on up. Once running- set up your wifi. Click on wifi-icon and log onto your network. Then "try" that linux out and see if you think you may like it- do not install it UNTIL you are satisfied that you want it. Once you are happy...then select the install icon on the desktop. Follow instructions. Then when it asks for a password- make one up and don't forget it. Let it finish the install- and enjoy it.
If you decide you don't want to install-- just back out and shutdown, remove dvd or usb...and you are back where you started.
Since you did not mention which linux....let me warn you....many linux os's are very user friendly, some even look similar to windows...and they are generally so easy to use you may wonder why so many reject it? BUT- some of the linux os's are for experienced users and you will really screw up if you try them. Stick with Ubuntu, Mint and that type that is made for the new user- stay away from Arch and Kali and that type.