You mine electroneum for free on your phone and you are aquiring electroneum which you can then sell on an exchange for any another currency such as USD, GBP, Euros. etc. The amount of electroneum that you mine and aquire through sharing this system with others will determine the amount of electroneum you earn.
The price of electroneum in terms of USD, GBP, Euros etc is driven by market forces. Right now the price is very low and you're able to see the current live price in your app at any time by clicking the Value tab. Electroneum is a new exciting currency which will increase in value over time so the important thing to do is aquire as much as possible for free now while you still can.
Remember that electroneum is a new currency launched in the latter part of 2017 and today is already worth more than double what bitcoin was at the same point in its development. Today each bitcoin is worth thousands of dollars. Of course we have no idea how much electroneum may eventually be worth, but we do know that the more electroneum that we have the more money we will make as the value increases, so we'd be crazy not to mine it for free on our phones and share it with others through this system.