Ethereum builds on the success of Bitcoin as a technology and cryptocurrency. They complement each other within the digital ecosystem. Ethereum or Ether or ETH is a "crypto-fuel". A digital token that pays for computation on the cloud and its not stricly a currency like bitcoin. You can:
Trade Bitcoin (BTC) for Ether (ETH) using most exchanges
Use Ether (ETH) as a pegged derivative. For example you can trade Bitcoins to an Ethereum token that always trades back to the same amount of Bitcoins while being traded in the Ethereum network via compatible contracts.
