There are four main ways to achieve lift. I know a bit about it and will attempt to clarify:
You can lift the suspension with taller leaf springs (a higher arch) and longer shocks. This can give you better articulation, or "flex". This is what a "suspension lift kit" generally refers to.
You can install a spring over axle (SOA) kit which will relocate your axle under your leaf springs to achieve 5" or so of lift and better articulation.
You can install longer shackles which will give you some lift (and can help taller leaf springs to articulate fully). Generally the most people lift with shackles is 1.5".
Finally, the body lift. It is just what it sounds like. You install longer bolts to connect the body to the frame with spacers between the body and frame. It gives you lift and wheel clearance.
Now remember as you lift that your driveshafts and other components are not being lifted, but are being stretched. Modifications will be necessary to keep from breaking driveshafts or u-joints. Installing a transfer case drop may be enough if you don't lift very high. If you do go tall, look into a slip yoke eliminator (SYE) driveshaft.
As you lift higher, you will also need longer connections in your steering components, brake lines, track bars, and sway bars. I recommend just removing the sway bars. Mine drives better, even on-road, without it. You could also remove the track bars, but some state inspections require them.
...I probably forgot a lot, but I don't really know that much. Hope it helps.