The difference is that the Ethereum platform is Turing-complete. Various new functionality can be developed with relative ease. This makes the blockchain Ethereum often also called programmable blockchain. While Bitcoin has only one function that aims to facilitate peer-to-peer transactions as a digital currency.
means Ethereum is better than bitcoin?
I think bitcoin is still the best right now, and besides I think it's just a confidence factor. bitcoin has greater confidence than ETH.
and also bitcoin is the first coin.
Yes bitcoin is good in that sense no doubt and that is the reason that still people have more trust on bitcoin than any other currency. But I think that we should also accept the importance of Ethereum which is providing assistant to people for developing their projects.