So you've clone a repo and there is a directory in it. Also, you have a file called
.gitmodules. Now what?
What you have is a reference to a git submodule. Look in the
.gitmodule file and your directory will be described there.
The next step is to initialize the submodule
$ git submodule init
Then you update the submodule to pull in files.
$ git submodule update