Clarinet reeds play a huge part in how you sound.
All musical sounds come from a vibrating source. In your case as a clarinetist, that source is your reed. When your airstream hits the reed, it vibrates and sends those vibrations through the rest of the instrument. The vibrations create sound waves and when they resonate through the inside of your instrument (the bore), that's what makes your clarinet sound like a clarinet (and not a flute or a drum or a tuba).
The reed acts similarly to your vocal cords when you sing. Air goes through your vocal cords, which makes them vibrate. Your throat and mouth cavities, like the bore of the clarinet, resonate the sound. The biggest difference is that your vocal cords control what pitch you sing, and on clarinet you control the pitches with your fingerings and voicing.
General Information About Clarinet Reeds
Most reeds are made out of a type of cane called Arundo Donax, which looks a lot like bamboo. The cane is cut into rectangular sections and then shaped and polished. Some clarinetists make their reeds by hand, but most of them choose to buy them.
Here's a look into how reeds are made at a factory:
While most clarinetists play on cane reeds (myself included), there are also synthetic reeds available. Some are entirely synthetic and others are simply cane reeds with a plastic covering. The idea behind synthetic reeds is that they'll last longer and play more consistently than cane reeds. On the other hand, synthetic reeds may not be as flexible as cane reeds and you won't be able to adjust them. I've only tried synthetic reeds a handful of times just in practice, so I can't personally vouch for them.
Clarinet reeds are divided into strengths, which refers to how thick the cane it comes from is. All reed brands that I know of offer a variety of reed strengths, usually shown by a number on the box and the back of the reed itself. The numbers usually range from 1 (thinnest) to 5 (thickest) and include the half numbers as well (i.e. 2.5). While each brand varies in what strength number the assign to the different thicknesses, beginners usually start with a 2.5 to a 3.
Buying Clarinet Reeds
When you're buying your first clarinet reeds, you might feel overwhelmed with the amount of brands available to you.
Here are some of the more popular reed brands:
Reeds usually come in packs of 5 or 10. I order several 10 packs online (usually enough I can get free shipping) and then I'm not running to the store every week for new ones. Also, no two cane reeds are exactly alike, even if they're from the same box, so it's a good idea to have a lot of reeds to choose from.
Breaking in Clarinet Reeds
When you first start playing on a new reed, you have to break it in. This gives your reed a chance to change and react to being played slowly. For the first few days you play on it, don't play for more than a few minutes and avoid playing in the upper register or excessive tonguing. Take note of how soft or hard the reed feels and how well it responds when you want it to sound. Repeat this process every day for 3 or 4 days.
Rotating Clarinet Reeds
Don't play on the same reed day after day! Rotating at least 4 reeds at a time keeps you from overusing any one reed. Plus, whether you're still developing your embouchure or you've been playing for years, rotating your reeds keeps your embouchure flexible to the subtle differences between reeds. Even if you find the perfect reed, it won't last forever.
Storing Clarinet Reeds
The tip of the reed is the most important part since it is the part that vibrates. So, protect it! Invest in a reed case and it'll help keep your reeds in good condition, extending their usable lives. Plastic reed cases that hold 4-5 reeds are a great choice for beginners. As you get more advanced, you may want to get a glass-bottomed case as they are great for keeping the tip of the reed flat in storage.