The OS X user-level Library folder (/Users/<your short name>/Library, or ~/Library for short) is hidden by default in Lion.
The Simplest Option
If you're in the Finder, hold down Option (Alt) and hit the "Go" menu in the menubar. As long as you're holding down the Option key, the Library will appear in the list of locations in the drop-down. Select it and a Finder window will open up on your Library folder.
From the Terminal
The Library isn't hidden from the Terminal; you can see it and access it just like normal. It's worth remembering, though, the OS X open command, which will open applications, files and — get this — Finder windows on folders. So, if you're in the Terminal and want a Finder window on your Library, all you need to type is:open ~/Library
Reverting To A Non-Hidden Library
alexLap$ ls -lOd ~/Library/ drwx------@ 74 alex staff hidden 2516 18 Jul 15:26 /Users/alex/Library/
chflags nohidden ~/Library