Does the “Library” only corresponds to the Fonts folder in Windows?
When installing a font, do I have to restart Windows?
No, the Fonts folder in Windows only contains installed fonts. The MainType library is a list of all the folders which you have told the program to scan for font files.
do when installing a font, I have to restart Windows?
You shouldn’t have to restart Windows, but many programs need to be restarted before they will ‘see’ newly installed fonts.