How does ChangeNOW work?

So, I'm curious about ChangeNOW. Can you explain to me, in simple terms, how exactly does it work? Is it a direct exchange platform or does it use intermediaries? How does it ensure security for its users' transactions? And how does it determine the exchange rates for the different cryptocurrencies it supports? Lastly, are there any fees associated with using ChangeNOW, and if so, how are they calculated?