Long /Short Variance Swap

Could anyone advise when to go long on variance swap and short on variance swap? Is it based on increase volatility ?

How is the payoff on a variance computed?

No, I know payoff formula. There is a question in CFA mock paper and they have used long variance swap I wanted to know when to use it with respect to volatility? As per the question short term volatity is increasing

Take a look in the curriculum.