The "little brother" to the tuba, the baritone or euphonium has a mellow sound and big range. Practice lip slurs often to increase your upper and lower note range. No gum or soft drinks before playing, please. Sugar mixed with saliva builds up on the keys and causes them to stick, making it difficult to play the instrument.
The first video below has been filmed in front of a mirror, so it's backwards. Make sure your left hand is "hugging" your baritone, while you put your right hand on the valve buttons.