What is Ether
“Ether is the fuel that makes Ethereum go.”
Ether is considered a currency within the Ethereum technology and is a necessary function (commonly referred to as the gas) to employ all the actions that support Dapps, Smart Contracts, and other tools. In order for any function to occur on the Ethereum blockchain, there needs to be gas to push them along. Smart Contracts and Dapps all need Ether in order to make them work.
Ether is to Ethereum as gasoline is to a vehicle.
Any developer who plans to build a Dapp, or wishes to access Smart Contracts on Ethereum, will need to possess Ether. Users can obtain Ether by mining or purchasing. Mining is the more complex of the two and often requires more of a cryptographic background. The easiest way to obtain Ether is similar to how you would purchase gas for your car. There are a few Ether exchanges where a user may purchase their Ether with fiat (government currency) or virtual currency.
Simply put, if your mail was a Dapp or Smart Contract you would still need to pay the postage to send that mail. Ether is the payment facilitator to make sure your Dapps work and your Smart Contracts are executed.