Here's a very brief introduction:

Bitcoin is the first cryptocurrency. Cryptocurrencies are a new kind of digital currency that even strangers can safely send and receive without relying on banks and governments (decentralized currency). An illustrated guide to Bitcoin and Cryptocurrency.

Ethereum is a platform for creating decentralized applications and uses a currency called Ether. In the same way that Bitcoin has decentralized money, Ethereum can decentralize anything. An illustrated guide to Ethereum.