Well, there's a lot of things to know about getting into string bending using benders. I've owned three types so far, and I'll tell you about them, but understand I'm no expert at all. I'll tell you where the experts are in a little bit. But I'm not only not an expert, but I'm also not what you would call any good at string bending with these devices, either- I'm still learning. A lot of what I'm learning is what does not work for me.
But a bender was designed to emulate what a pedal steel guitarist is able to do, bend one not up and not the others in order to make new chords and play melodies easier. Bear in mind that the pedal steel is played with a slide, so some kind of method would be needed to give that instrument more versatility.
Where a whammy will affect every note that is being played, a bender does not. This can emulate a pedal steel somewhat and also just add some cool and otherworldly sounds (this is my hope, anyway).
My current guitar with a bender is this Telecaster:
It's all Hipshot stuff. The B bender would be controlled by means of activating a lever with your hip (hence the name) and would fit through the loop you see by the strap lock. The G string can also be bend on this guitar, by using the lever you see jutting out from the device.
The other three levers are drop tuners, which will put the guitar into open G tuning very quickly. But the benders are what you see there. Here's another look:
I also used to own a Telecaster with a strap activated bender, the kind that you would most usually see. I didn't get along with it, although I wanted to. I sucked at the bender and also didn't get on with the neck of the guitar, for some reason, so I sold it on years ago.
I later bought a Casino in order to use a Bigsby Palm Pedal on it, which is basically two hand activated levers:
I didn't like much about that bending system, it was hard to use, the levers were in my way constantly. I also didn't like the neck on the Casino, so I gave it away. But some folks cut the levers down on these types of benders, I didn't feel like doing that, and I just shed the guitar.
But I'm not soured on the concept, here you will see that I have another Hipshot device ready to go. This one will be both the B and the G string activated by levered benders:
The reason being that this way, the levers can be moved out of the way when not in use, which will be often. Using a string bender isn't easy for me.
But what you will want to do if you want to learn more about them is, go to the "*****" forum, which is designated for Telecasters. There is also a subsection devoted entirely to benders, with a lot of very knowledgeable people who can help anyone learn a lot more then I ever could. Also, check out "Rolling Benders" for a new and non obtrusive option, as well as any number of other systems in place.
Hope this was helpful!