I can't help wonder sometimes, say I have 10 BTC in X address, if I send them to Y address, I have 10 BTC in the wallet with the Y address.

Say I create another address for the same wallet with Y addy, will anyone be able to know if I spend some of that 10 BTC?

If yes can you please explain how? It's still unundeerstandable for me, since the blockchain only deals with addresses, how can btc be linkable to wallets?

Other than that, if I send the 10 btc to Y address, will anyone be able to get all the addresses of the same wallet? Thanks!