They’re very similar but in performance mode you can have the FX assigned to it be touch sensitive. So to set it up you hold down function + the pad you want to assign the FX to, and while holding it change the knobs which control the FX you want to be assigned to the pad. So for example, holding down the performance pad and moving the pitch of a kick up 12 semitones will assign the pitch of the kick to the performance pad. Then when you alter the pressure on the performance pad you’ll find the pitch of your kick moves up based on how hard you hold it down.
Scene mode is set up in the exact same way but it’s static. So, if you were doing the above, when you hit the scene pad your kick would just move up an octave once the pad is hit.