In Solidity there is msg.sender whose value may be used to send Ether to the sender of the msg.
How the wallet to send money is chosen when the sender has several Wallets?
Is there concept of account in Ethereum or is "account" a feature of Ethereum Wallet program not of Ethereum itself?
That is, how accounts and wallets are related?
An account for solidity is defined by its address. You can send the money only to an account.
The account can be contained in a wallet or no, it doesn't matter. The wallet is a way create or manage your account or multiple accounts securely and easily. You can also create an account manually using geth, you don't need to have a wallet to do so.
