why Chrome pop up from gocomputerhelp247.com/system-alert
It is a form of scripted scareware. Someone programmed that pop up message to scare you into wanting to buy a "fix" or perhaps to cause you to stay on a page long enough for them to install malware. 

It should be safe to shut down your mac normally (perhaps after taking a picture of what’s on the screen) and then sharing that image with someone you trust on computers and leave the mac off until you’re comfortable about your backups or what plan you have to get any malware removed.

Why not do some research on malware and ask a follow on question if the article you found doesn't do a good job of educating you about Internet security and malware.