How to re-install an OS on Mac My friend has a Mac book pro. I'm afraid I know nothing else about it.

For reasons unknown, and I dare not ask, she decided to rub a magnet over it, beside the touch pad. 

She heard a strange noise, and powered it off. Then, when turning on, she just saw a question mark on the screen.

I'm guessing she's either wiped or destroyed the SSD. However, she's asked me to restore it and I know nothing about this. 

Whilst my research shows me that files may have been synced to the Cloud (the cloud? Surely they mean to a server, using the technologies which have been available for years). But it doesn't state if the OS is backed up.

The computer didn't come with any discs. 

On a Windows PC (which I have little experience with), I know that some times the OS isn't included but the serial number is, so you can get an ISO and re-install it that way.

Other PC's include the installation files on a partitioned hard drive.

My question is, is there a uniformed way Apple supply the OS with Mac products (unlike PC's)? If so, what is it?
The question mark comes up when the start up files have been messed up.

I do not know if you can repair the Magnet damage but you can try to restore.

Mac's have a Restore function build in (or online)

To access start computer and hold cmd-r

that will bring up the restore menu.

Depending on your computer model you might have the Internet restore option.

The sound you heard was the forced computer shut down.