how do i back up my iTunes library on windows computer?

See Backup your iTunes for Windows library with SyncToy - Apple Community.

Keeping your library only in the cloud is a recipe for disaster, but if you want the ability to have the same library on multiple computers or devices then iTunes Match or Apple Music might suit you. Make an offline backup before you start. You may potentially want to main a separate cloud library.

tt2

Copy your entire iTunes folder to your backup destination.

Now at first you talk about backing up then you talk about "putting" which is not the same. What are you trying to do?