Some things to remember:
1-3rd party interfaces often have software for routing and monitoring(JFreak already mentioned)
2-With Pro Tools open, go to Setup>Hardware and make sure the Focusrite is the selected "audio engine"
3-Open setup>IO>Input tab and make sure that the Focusrite inputs are listed and "dotted" on the routing grid.
4-remember that youtube is a pretty great source of tutorial videos to help get you going
