There are a few different levels of "pumping".
To launch your board onto a plane, you get back and get the nose up
so the board can plane off efficiently, then you can do 2 or 3
full body, put everything you've got into it pumps. The rig starts out sheeted out and you pull it back and in as hard as you can.
This does 2 things. First , pulling the rig back and in really hard kinda "shoots" the board forward and this may be enough to launch you onto a plane. t
The 2nd thing that happens is when you put all your effort into bringing the rig back and in rapidly, your weight comes off the board, helping it to "jump over" it's bow wave and onto the plane,
Once you've launched, you can do some "flutter pumping" where you work the rig in and out, nearly fully sheeted in, to kind of "shake" the board loose and get it to accelerate even more.
Last type of pumping is "fin pumping' where you push across the top of the fin with short "jabs", the idea being that you can help the board unstick and get going even faster.
Hope this helps,