this is cold water soluble, albeit fairly reluctantly so. Most shop stuff is only hot water soluble.
there are other threads on here about using it successfully but to recap
1. mix the mousse powder with the shakes powder
2.add cold water & mix with electric whizzer for at least a minute.
3. pop in fridge for 10 mins.
if the resulting mousse is firm & fluffy you've done it properly ,if its all froth on top & liquid below then it wasn't whizzed enough.