Glad that I answered you well.
On a centralized exchange like Binance, when you own 1 ETH doesn't mean you own it. What Binance would do is buy 1 ETH on the Ethereum blockchain for you and keep it in its own wallet. After that on Binance platform, Binance tells you that you own 1 ETH which can be traded on the platform as if they are real ETH.
Regarding BETH, what I understand is during network upgrade from Ethereum to Ethreum2.0, all ETH have to be locked, and can't be traded. As Binance being an exchange it wants to allow keep trading, holding or staking on Binance so that created a wrap token called BETH, for every BETH, 1 ETH is locked on Ethereum blockchain so that you can keep doing as before.
Hope this explain well.
!CHEERS
!BEER
!WINE