Let’s start with this. There are three types of power. Apparent power (KVA), Reactive power or wattless power (KVAR) and Active power or useful power(KW).
Let’s take an example of the motor. Electricity board provides us KVA. As we know we need to set up magnetic field within motor for conversion of electrical energy to mechanical energy. Part of KVA i.e. KVAR is used to create a magnetic field. remaining part of KVA i.e. KW is used for actual work i.e.converted into mechanical work.
So if there are two motors one new and one old, both will be charged for KW that they are using. Even though later one is absorbing more overall energy from the supply.
Whereas in industries, the strict restriction is put on the absorption of KVAR also as it leads to many other ill effects like more losses in the transmission line, poor pf etc.
So in the end, KVA is total power supplied and KW is the actual energy used.