reading all those technical things is confusing me more
It's a bit confusing indeed but after making few transactions on both chains things will become clearer.
just is simple layman term , when receiving coins in bsc i have to remember one address only
and i can get every coin in bsc with that address
The answer for both questions is yes. The same seed or private key will generate the same address for both networks (ethereum and bsc). But to see your tokens on Metamask (or any other wallet) you need to add bsc to it so it can connect to the bsc network and interact with it.