Ethereum is a public blockchain whose native coin is called ether, usually written ETH. Unlike Bitcoin, the chain does more than move its own coin: it runs small programs called smart contracts, and many tokens live on it, including the ERC20 version of USDT. Every action on Ethereum is paid for in ETH, even when the thing being sent is a token. A wallet that holds only USDT on this chain cannot move it without a little ETH beside it. The price of ETH moves up and down like any other coin.
An Ethereum wallet is an app or device that holds the keys to an account on the chain. The ETH and tokens stay recorded on the network itself; the wallet shows them and signs transfers. A new wallet displays its recovery words once, and those belong on paper, away from the phone. An ETH wallet address starts with 0x followed by forty hexadecimal characters. Several compatible chains use exactly the same format, so a 0x address alone does not reveal which network a transfer will travel on. The network name has to match on both sides.
Litecoin is one of the oldest coins, built on the Bitcoin design with changes that produce blocks about four times as often. On the question of Litecoin vs Bitcoin, Litecoin tends to confirm sooner and to charge lower fees, which is why some casinos accept it for deposits and withdrawals. It runs no smart contracts the way Ethereum does; its job is mainly payments. Its price swings like any unstable coin, so it suits moving value more than keeping it steady. A cashier usually states how many confirmations it waits for.