ETH is a native coin of the Ethereum Blockchain.
Ethereum lets people who don't wanna develop their own blockchain create and run tokens on their blockchain but in return asks these tokens to pay some fee. And this fee is paid in Ethereum's native coin which is ETH.
ERC-20 is a code name for all tokens created and run on the Ethereum blockchain.
Since all ERC-20 tokens run on Ethereum, they all can be stored in one wallet address. It's like living in a 100-story building. Even though there live thousands of people, the building address of them all is the same and they all receive emails to the same building.
This is why sometimes you can see different tokens in a single wallet on Etherscan:
So, whenever you move an ERC-20 token from one wallet to another, you pay a fee. This can be from a wallet to another wallet, from a wallet to an exchange, from a wallet to a smart contract, and vice versa.
When moving them out of an exchange, normally, these exchanges charge you (for the fee) from the token you are moving out instead of the native token of a blockchain you're using. Because they know it's a hassle and made it easier for the user. On the contrary, you have to have some native coins of a blockchain you're using when doing a transaction between two wallets to pay the fee, which is exactly your case.
Just get some ETH using Binance, and send them to the wallet address you have your USDT inside.