Ethereum Basics

At its elementary, Ethereum is an open software platform based on blockchain technology, just like bitcoin, but with some major technical improvements.
While the bitcoin blockchain is knowing to track ownership of digital currency, the Ethereum blockchain allows developers to build and manage decentralized applications.
In the Ethereum blockchain, instead of mining for bitcoin, miners work to earn Ether, a crypto token that feed the Ethereum network, transaction fees and other services.

Infographic below "A begginers guide to Ethereum" will explain you more details (source).

More reading about crypto:
Cryptocurrencies in free fall
Iconomi In A Nutshell
Pros & Cons About Investment In Cyptocurrencies - part 1
Pros & Cons About Investment In Cyptocurrencies - part 2
Blockchain Explained
Smart Contracts Explained
How the Bitcoin protocol works and what blockchains are