The foundation directory is a Guava package.  If you are running the Guava Application Framework & Environment, you can install this package to provide a distributed connection to a Foundation source.  You are required to have the Foundation PHP API in your PHP's include path.  Configuring the package gives you the ability to connect to a specific Foundation source.  By communicating with the System Module provided, you'll be provided with a reference to the database connection which you can then use with the Foundation API.

INSTALLATION:
Copy the foundation/ directory to your Guava's packages directory.  Go to Package Administration in Guava and install the package.  Afterwards, you must configure the Foundation data source before using it in other packages.