The user library folder is stored at the path /Users/<username>/Library/. The way to access it is different depending on which version of macOS you are using:
macOS 10.12.3 and Later
The Library folder is hidden by default. To open it, click on Finder in the Dock. Click on the Go menu at the top of the screen, hold down the Option and Shift keys, and then choose Library. (Only one of Option and Shift is needed, but due to an OS bug, which one you need to hold down can vary. Thus, it is easier to hold down both.)
Another way to access the Library folder is to choose Home from the Go menu, then type Command-Shift-Period to show invisible files, and then open the Library folder.
Mac OS X 10.7 Through 10.12.2
The Library folder is hidden by default. To open it, click on Finder in the Dock. Click on the Go menu at the top of the screen, hold down the Option key, and then choose Library.
Another option is to go to your home folder, choose View ‣ Show View Options and then make sure that Show Library Folder is checked.
Mac OS X 10.6
Click on Finder in the Dock, click on the Go menu, and choose Home. This will show your home folder, and you can open the Library folder directly.