Vincent,
Have you looked at the examples here - http://docs.strongloop.com/display/DOC/Example+applications
There are simple applications here including a simple mysql applictaion that explains how to connect your data via a connector.
https://github.com/strongloop-community/loopback-mysql-example
You can peruse the forum threads here too.
https://groups.google.com/forum/#!forum/loopbackjs
hth