Ethereums main foundation is to become a ''world computer''. This is simple terms that means that all the clouds and servers would be replaced by concepts called 'nodes''. A node in simple terms is a connection point. While third parties control our information at the moment, the purpose of Etherium is to give people control over their own information and combine all your own devices and any changes saved will be changed on all these devices by means of nodes.
In order to buy Ether, you must find someone who has it and wants to trade. You can do this by either directly in cash or via bitcoin. Once the person has Ether they can either create or join contracts. this will automatically execute the terms of the contract and not depend on third parties. Or you could buy ethereum directly form an exchange.
How ethereum is used
it's a very simple concept that is quicker and efficient than banks or any third party's. Ether has two types of identification like digits. theses are the public key and the private key. in order for the user to get paid or get money transferred into their account they just need to give the public key out, but in contrast, if they want to pay for something they must sign them over password.