The clarinet is a family of
woodwind instruments that have a single-reed mouthpiece, a straight
cylindrical tube with an approximately cylindrical bore, and a
flaring bell. A person who plays any type of clarinet is called a
clarinetist or clarinettist.
Clarinets have the largest pitch range of common woodwinds. The intricate key organization that makes this range possible can make the playability of some passages awkward.
To play the Clarinet one has to take it into their mouth with the reed on lower lips, the mouthpiece touching the upper teeth. Few clarinetists will bend their upper lip over the teeth as well - this will not change much for the listener's, only for the player's subjective sound impression (the sound waves don't get into the inner ear so directly via the scull as without).
How far one puts the instrument into their mouth depends on the size of your mouth and the position of your teeth. If one holds it too deep into their mouth, they cannot fully close their lips around to stop air breaking out at the mouth corners. This requires guidance from expert trainers who make this erudition simpler and further pleasant and exciting.