why cannot I see Library folder under my home directory in Finder?
Yes, that folder is hidden by default along with another bunch of files and folders becasue most users never need or want to go into it.
To make it visible press:
ShiftCommand . 
That's Shift-Command-Period, it will reveal all the hidden files. There is also a command to un-hide just the ~/Library folder:
chflags nohidden ~/Library