I'm unable to hear the imported MP3 through my headphones

[joshmattg]

Hey guys, I'm new here! I'm working my way through Pro Tools Express and there's one thing that I can't figure out for myself. All I would like to do is record my own vocals to standard backing tracks that are imported into Pro Tools Express. There's only one thing, the recorded vocals and the backing track are playing through the speakers on my computer instead of playing through my headphones. Is there something that I need to do in order to change the signal because I can't go any further at the moment. I've had a look on the internet but I can't find anything too specific. Any help is much appreciated!!