The
tilde at the beginning of the path represents your home folder, the one containing your Pictures, Documents, Movies, etc, folders.
To access directly a path, the simplest way probably is to use the "Go to..." command of Finder's "Go" menu and to copy and paste the path.
(not sure about the exact menu names)
Once in the folder, you just have to move the .qtz file into it and relaunch Pixelmator.