Why don't we just get more into it so it's all clear. And I'm bored so here we go...
On 4x4 trucks only, you have torsion bars in the front to provide lift and spring rate suspension. The bars twist according to the amount of load put on them (of off if you lift on a bump or something). They are under considerable pressure and can be adjusted up or down to create height and also tension/spring rate increases/decreases.
When you get a "normal" commercially available lift kit, you'll be getting a bracket that actually LOWERS your front differential to keep the axle stubs and Constant-Velocity (CV) joints in line. The torsion bars are then cranked up to get more lift out of it.
4x2 trucks DO NOT have torsions; they have coil springs only.
On the rear, a shackle connects the spring to the frame, and provides for extra spring flex. You can get longer-than-stock shackles to lift the truck a bit. An Add-A-Leaf spring is just an additional spring pack (individual or group of spring leaves) that provide extra lift and a stiffer ride. The AAleaves tend to be an extra overload spring and make for a stiff ride you may not want unless you are towing frequently.
For lift options in the rear. You can go with the add-a-leaf (cheap but I never recommend them), shackles (the lesser of two evils), blocks (NEVER!), or you can order some longer springs which will lift your truck the "right way". I highly recommend you check out National Spring in El Cajon or Deaver Spring in Anaheim, I think... Deaver being the better recommended. They can set you up with springs to your specifications -- lift, amount of weight you plan on carrying, stuff like that... and for $400-500, you just can't lose!