Bends are pretty easy. As you're playing a note, you just relax your lower jaw and loosen your embouchure. You need to listen as you do, so you can get the kind of sound you want. You're basically using your mouth to make the note become flat. The speed with which you do so depends on the type of effect you want. Then you firm up the embouchure to bring it back into tune.
Scoops are where you loosen your jaw even before you start the note, so when you do blow the note is already flat. You then quickly bring your embouchure into correct playing position so the note becomes in tune.
To growl, all you have to do is to hum while you play. It doesn't matter what note you hum. You're basically creating an acoustic interference in the air stream which affects the tone quality of the note. The effect is a very rough sound.
Though these dramatic devices aren't that difficult to perform, they do take practice. Some will come easy, some won't. (I once had a student who got so frustrated with trying to growl that he wanted to give up. But I kept him at it, and he eventually got it.) You've go to know what you want it to sound like in order to attain that goal. It just takes time.
When starting to learn these techniques it sometimes helps to use a little softer reed.
Bends and scoops will be easier, and if the breath support goes a little 'soft' during growling practice you'll still be able to get a decent result.
Once you get everything under control it won't be too hard transitioning back to your regular reeds.
Depending on your experience level it may be a bit early to worry about scoops and bends, but there are a couple of things you can do to give you a feel for the concept, even if you're not able to make it sound very good for now.
Just to get the idea...play a note in tune as you normally would...then relax your lip and let the pitch go as flat as you can. (It'll probably sound terrible, but it doesn't matter). Then slowly tighten back up to return to your original "in tune" embouchure. Do that for a while until you get the hang of lowering the pitch and then bringing it back in tune. After you get the hang of it, try starting the pitch as flat as possible instead of starting out in tune...then bring it up to normal pitch. After that, you can move on to starting out by fingering the note a half step below your target pitch...starting that note flat as well...and slowly raise the appropriate key to the target note's fingering while simultaneously tightening your embouchure to bring the target note up to the proper pitch...(the same way you did when you started out flat on just one note and brought it into tune, but it will be even more exaggerated now).
That's a very basic description of what's involved, and it will take a while to make it sound good...but essentially, that's all a scoop is...a smooth but exaggerated raising from one pitch to another. I hope that helps.
And I see I've basically just repeated what's already been said.
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