This is a simple feature which allows you to see realtime exchange rates between different currencies.
The top row is the currency you want to convert into others, the rows below show what the value you entered is in different currencies, i.e. here 1 GBP equalled 1.1561 EUR and 1.3632 USD, as well as 0.000015967 BTC!
By tapping on one of the other currencies, you will move this to the top so you can use this as your base.
I have started sliding the BTC row to the left so it shows some red on the right. Sliding it to the left deletes it from your list of currencies in the calculator.
You can add any other currency by pressing the ADD CURRENCY button.