Two library folders found in Macbook HD? the other is under system

there are more than two, actually. there is a library folder in /Systems. *DO NOT* touch that!. these are system files. there are a library folder at the top level of the drive. do not touch that unless you know what you are doing. there is also a library folder in your home directory. that contains various user preference files. if deleted they will be recreated with default settings but you can loose data that way so don't touch those either without need.

Does anyone know what these two library folders do?

One is meant for files to be accessible to all users and changeable by administrators, while the one in System is used by Mac OS X itself. Both are necessary for Mac OS X to function properly.

(49769)

Yup, the 3 folders are:

/Library (At the root level of the Macintosh HD)
~/Library (Within each users home folder)
/System/Library

The first two can be removed and rebuilt without a complete re-install of the OS, while the System folder contains all the required files needed for use by the operating system.

One of my kids has moved one of the libraries by mistake and now when I restarted my mac....all previous settings had gone and I've had to start almost as a new user. All preferences and downloaded fonts are no longer there. Software wont open....Can I locate and drag the library back to where it is supposed to live? Will these settings then return if I reboot.

Where do I find the missing library?