How is the commission calculated?

Question

Cryptocurrency

Could you explain to me how the commission is calculated?
For example, here is the code from the vex exchange for the btc_usd pair.

{
    "server_time":1370814956,
    "pairs":{
        "btc_usd":{
            "decimal_places":3,
            "min_price":0.1,
            "max_price":400,
            "min_amount":0.01,
            "hidden":0,
            "fee":0.2
        }

Commission (fee) 0.2. What is it? From what amount is the calculation? When charged - when buying, selling, placing an order...
On the exchange they write:
---
Commission for trading
Commission for trading for all currency pairs is 0.2%.
---
I.e. how is the calculation? Issuing an order will deduct - 0.2% of the invoiced amount? And the cancellation of this order will deduct another - 0.2%?
If not difficult, please give an example.

Answer 1

well, you declare the amount in a currency, here in this currency 0.2% and they will take
it upon cancellation, the entire amount is returned, why would 0.2%, for which service?