Copying the lib directory into your include path and requiring the lib/autoload.php file should be enough to begin using phpcassa. This will not automatically allow the C extension to be used, though.
The C extension is crucial for phpcassa’s performance.
You need to configure and make to be able to use the C extension:
cd ext/thrift_protocol
phpize
./configure
make
sudo make install
Add the following line to your php.ini file:
extension=thrift_protocol.so