Ethereum is a decentralized platform that runs smart contracts: applications that run exactly as programmed without any possibility of fraud or third party interference.
Ether, the native cryptocurrency of Ethereum, powers the Ethereum network and is used to pay for transaction fees and services on the Ethereum network.
NOTE: WARNING: Purchasing Ethereum in cash is not recommended as it is a risky and unregulated form of cryptocurrency transaction. There is potential for fraud, scams, and money laundering. It’s important to be aware of the risks involved before engaging in any cryptocurrency transaction.
You can buy Ethereum with cash using a peer-to-peer exchange like LocalCryptos or BitQuick.
LocalCryptos is a person-to-person marketplace that supports over 150 payment methods, including cash. BitQuick is a US-based service that allows you to buy Bitcoin with cash deposited into a third party bank account.
Once you have Bitcoin, you can use an exchange like Coinbase to convert your Bitcoin into Ethereum.