You let your lower lip, supported by your teeth, vibrate on the reed.
I suggest you ask your band instructor or a musical instrument store to let you try a clarinet.
How do you blow into the clarinet? I know w/ the either the trumpet or trombone you have to kind of make a sound like a duck or something. What about the clarinet?
2 answers
When playing a brass instrument (trombone, trumpet, etc) the lips vibrate in the mouthpiece and that is amplified and comes out the end. Fingering changes the length of the column of air and that changes the pitch. In woodwinds (clarinet, saxophone, bassoon, etc) the mouthpiece is placed IN the mouth (as opposed to the lips being placed in the mouthpiece of brass instruments) with the bottom lip curled over the lower teeth. The musician blows and a reed vibrates. The vibrating reed then is amplified and the sound comes out the end. Again, fingering changes the length of the column of vibrating air and that changes the pitch. I recommend you ask around at school (band director, music director, or whomever) or visit a music store that sells instruments. They can show you the correct way to use the instrument and how it sounds.