Are you asking what to assign to which pad, or how to determine which notes and channels the pads are set up for?

Just how to set up reaper so when I plug it in I can control the vst with it in reaper.

I just plugged mine in, opened Reaper, then a) enabled the port in Preferences/Audio/MIDI Devices, b) selected the device in my track input, c) loaded a VSTi and bashed those pads. Bigger pic: