Basing on a blockchain, Ethereum runs for managing decentralized apps or programs. Founded in 2014 by Vitalik Buterin and his partners, Ethereum helps anyone who wants to design a program, which is not controlled just by one person. Apps that are designed on Ethereum are identified as Dapps. If you want to write a Dapp, take into consideration that there isn't one person, who will control your app (even you won't have that privilege). Ethereum has its personal programming language, which you have to study for writing a Dapp. It's named Solidity.
To get it clearly imagine a lot of computers that work together as one powerful computer to manage one app. That’s what the Ethereum platform performs on Dapps.
See that Ethereum isn’t a cryptocurrency, it's a platform for making decentralized applications. But Ethereum has its own cryptocurrency, which’s known as Ether.
Ether was designed for allowing market relations in the platform. For operating with Ethereum platform you need power upped machines, enough storage, and many other tech tools, so Ether is a currency that lets you buy all this kind of things inside the platform. At first in 2014 one Ether was valued 40 cents, but it started growing in 2017.