Ether is the currency used on the Ethereum network and was proposed by Vitalik Buterin in 2013. Ethereum is also a decentralized network and allows smart contracts to be created on its platform so these can be executed without the need for a third party.
Ether was not created to be a digital currency but rather as an incentive or reward for a process to be completed in the Ethereum network. It is referred to as fuel because this is used to pay machines for executing a required process. The Ethereum network allows smart contracts to be created on its platform so these can be executed without the need for a third party.
It takes approximately 15 seconds for a block to be confirmed on the Ethereum network. Fees are calculated according to the complexity of the transaction (gas) and paid in ether.
You can switch between currencies from the Home screen, which is accessible by the back arrow found on the top left of any currency screen.