The choice you get is to save files or lose them for ever.
In both cases the Reset is designed to reinstall Windows 10.
Note: Some people claim they have ended up with an earlier installation of Windows instead (i.e. Windows 7, 8 or 8.1). That is not supposed to happen, but there used to be a roll back feature for this purpose. At this point you'd need to use a Recovery Disk (either via recovery partition, or DVD) to roll back to an earlier Windows edition, if that is your intention.
The information about recovery is on the website I all ready posted yesterday.