The .git folder does exist. You can't see it because the Finder hides files and folders that start with a period, like the .git folder. There are utilities you can download to show hidden files in the Finder, like Show Hide Invisible Files. Or you can set it in the Terminal. A Google search for show hide invisible files mac brings up many articles on how to show hidden files in the Terminal, including the following:
Quickly Show/Hide Hidden Files on Mac OS X Mavericks
Where the .git folder resides depends on how you created your git repository. If you created an Xcode project and told Xcode to create a local repository, the .git folder will be inside your project folder.