You can read baritone music in either bass or treble clef. If you have a bass clef part, it will be in concert pitch, so what you see on the page is what you'll hear when you play. However, if you choose to use a treble clef part, it will be in the key of B flat, and it will sound an octave and a second lower. The treble clef part can be good for people switching from trumpet, but the bass clef can eliminate your need to transpose.