There is actually a dedicated sub-forum within this one for Vamo and I'm sure you will find MUCH information there. As a Vamo user myself I can tell you that VW means the Vamo polls the attached tank, cart or atty to find it's resistance and then sets the voltage accordingly to give you your
selected wattage. Most users like right around 8 watts, adjust up or down to find your happy place. The big difference between VV (variable voltage) and VW (variable wattage) is that once you set your VW it doesn't matter what resistance (within limits) the device is you screw on to it... you can set the vamo for say 7.5 watts, take a few puffs off of a low resistance dripping atty, usually around 1.5 ohms, take it off and put on a 2.8 ohm vivi nova. You are still vaping at the same 7.5 watts.
Watts are a function of volts and resistance: Watts = (Voltage x Voltage)/Resistance
So for that same 1.5 ohm dripper in our example you would have to have a variable VOLTAGE device (or the vamo in VV mode) set to approximately 3.35 volts... (3.35 x 3.35)/1.5 = 7.48 watts
Still in VV mode and you put that 2.8 ohm vivi nova on it? You'd have to turn it up to 4.5 volts to get approx. the same: (4.5 x 4.5)/2.8 = 7.23 watts
In VW mode the Vamo takes care of that adjustment for you!
Variable Wattage is a nice "set and forget" technology, especially if you like to change between different attachments
(Oh, in case you were curios... Volts = square root of (watts x resistance) )