The bank buttons allow your controller to shift the MIDI data it sends from its controls and pads. The bank buttons themselves do not send MIDI data to the computer.
Example: You have a row of 4 pads, and the MIDI number for each pad as you go across is 1, 2, 3, 4. These MIDI numbers are assigned to bass drum, snare, high tom, and low tom sounds.
If you press the pad bank button of your controller, it will shift the MIDI notes of those same pads so that they now output MIDI numbers 5, 6, 7, 8. Now that the pads are outputting different MIDI notes, you could assign those notes to hi-hat, crash, ride, and china sounds.
This setup lets you toggle the bank switch to change what the same row of pads controls, enabling you to play a wide variety of instrument sounds using just a single row of pads.
If you are using MPC Beats, I recommend mapping the MIDI numbers of your controller banks using MIDI Learn.