I was watching a submersible documentary and they said the pressure at the bottom of the ocean is something like 1.4 tons, but there’s a lot of life on the bottom of the sea. how do they live without being crushed?
Well, I don’t know the specifics but basically they are built for it, and if they could, they might wonder how it is that we can survive up here without exploding.
I believe it has to do with them being filled with water at a roughly equal pressure…somehow.
Well, the liquid inside and outside their bodies is at equal pressure so they are not crushed. Remember, liquids are incompressable. They also don’t have the same types of air pockets are own bodies are filled with which cause us the traditional compression problems you are thinking of.
Finally, these creatures have specially evolved biochemistry and proteins that allows them to function in the extreme cold and darkness. The pressure and conditions themselves helped shape this evolution to the creatures you see today.
They started that way… I know that’s a glib answer, but it’s the root of it all. When Creature J was made/born/spawned (lesse, tubeworms, fishies, crabs, worms, probably lost of other stuff), its body was already pushing out with the same pressure - that is, it’s MADE of its surroundings. And over time as the little J grew up,m adding more local mass to itself, its pressure outward remains pretty much the same.
This is why, when you try and take one of these creatures up to the surface, they explode - they are still pushing outward at 1.4 tons/sq in or whatever, while we’ve only got sea level atmospheric pressure on the surface.
I dunno how anything got DOWN there. Then again, I dunno haow anyting got started up here either.
I suppose ya start with a humble sulfur-eating heat-loving bacteria and move up from there, and everntually you’ve got an intersting ecosystem.
Another angle is to consider that they don’t have air in them.
We live under a “sea” of air with a 15lb force pushing on each square inch of our bodies. Shouldn’t we all be crushed? 
Just for comparison, a one-inch rod made of lead must be THREE FEET long in order to weigh 15lbs. Lay down on the ground and have someone stack 3ft lead rods all over you (or pile lead bricks on you to a height of 3ft.)
If you can explain why 15PSI doesn’t crush YOU, then you’ll know why a much higher ambient pressure won’t crush you either.
Stress management & Prozac. 
There are aquatic mammals known to dive several thousand feet on a gulp of air, So absence of air does not explain it.
Absence of lower-pressure air does, however.
Try this for an experiment: Go to the top of Mount Everest (okay, so it’s more of a thought experiment), and fill up a balloon with Everest-level air pressure. Expand the balloon to, say, a foot in diameter. Then take that balloon back down to sea level, and the extra pressure will cause the balloon to compress to, say, 8 inches in diameter.
It’s not that deep sea creatures don’t have pockets of air, it’s just that the pockets of air they do have are ALSO at a pressure of 1.4 tons per square whatever (foot? inch?).