Clarinet’s are woodwind instrument with a beautiful, round sound. Clarinets have the one of the largest ranges of pitch of all musical instruments, which makes it one of the most interesting and challenging instruments to play. Most schools have bands that allow willing students to learn how to play. If you are no longer in school, though, it is certainly possible to take lessons and learn how to play the clarinet.
Buy or rent a clarinet so that you can practice. Remember, if you're a beginner, expensive clarinets won't be practical or easy to play. It's better to rent or rent-to-own a cheap, used clarinet to begin. There are many good models which are easy to play. A Selmer plastic clarinet or a wooden Buffet E11 are widely used as beginning clarinets. If you are an intermediate player Cecilo clarinets are the perfect choice for you.
At your local music store, find out if they offer lessons. It's best to start out with a teacher instead of on your own so that you won't miss anything or learn anything wrong. Often, school music teachers will offer lessons for cheap.
Put the clarinet together. Attach the bell on to the bottom of the main part of the clarinet. Then slide the barrel on the top of the main part. Attach the mouth piece on that. Soak the reed in you mouth and slide the ligature over the mouthpiece. Slide the reed between the ligature and mouthpiece, with the flat part facing in. Tighten the nobs on the ligature until it's tight enough not to fall off. Remember to not tighten it too much, because it could put strain on the mouthpiece.
Curl your lower lip over your lower teeth enough to where your teeth won't dig into the reed (but not too much!) and place the mouthpiece in your mouth with the reed-side down resting on your bottom lip. Keep your jaw flat. Your top teeth should be planted firmly on the top of your mouthpiece (opposite of the reed side). Your upper lip should be normal, unless you wish to play what is called double-lip (curling upper-lip as well). For beginners, only curling the lower lip is best.
Seal the corners of your mouth around the mouthpiece. If your lips aren't sealing it enough, air will escape and no sound will come out. Try to lift the corners of your mouth to tighten it even more (though this may be hard to get used to at first and you will probably learn it best by taking lessons). Your tongue should be pointing at the reed when you play, but not touching it. When you blow, be sure not to puff out your cheeks!If you produced a sound without covering any holes or keys (a non-squeak sound, that is), this is what is called an open G on the clarinet. On the staff, it is on the second line from the bottom. Because the clarinet is in the key of Bb, it is what is known as a transposing instrument, meaning that it is not in the concert pitch of C (some instruments in C - piano, flute, oboe, guitar). This also means that any note you play on clarinet is two half-steps lower in concert pitch. If you squeaked, don't be discouraged! It's hard to get used to the clarinet embouchure (mouth shape). Just keep trying!
You should check out your local music store again and see what kinds of beginner clarinet books they have. Some commonly used ones are Band Expressions, Standard of Excellence, and Rubank Elementary Method. All of them will teach you how to play songs and such, but a teacher is best for mastering technique and your sound.
Be patient! The clarinet takes time to master so don't get discouraged if you don't get it right away.
Relax! Stressing over playing the clarinet will only result in upsetting yourself. If you find that you are getting frustrated, take a break and come back to it. Relaxing yourself may make playing feel more natural.
Enjoy it and have fun!