The Account tab provides tool to handle your different Monero accounts within your wallet. Each wallet can have multiple accounts, and each account has its own balance. Also, each account can have multiple subaddresses associated with it. For convenience sake, the account address is considered the first address (or subaddress) generated for an account. Since accounts and subaddresses are deterministically derived from the mnemonic seed, you only need to know the seed in order to restore the account/subaddress structure when restoring a wallet (although any labels you assign to the accounts/subaddresses will need to be added again, since they are stored in your wallet file, and not in your mnemonic seed, neither on the blockchain).
(1) Balance All: Let you see the sum of all your accounts balances, unlocked or not.
(2) Accounts: This is the list of all accounts already generated on your wallet and their corresponding account addresses.
(3) Create new account: Click on this button to create a new account and set its optional label.
You can change the current account by simply clicking on it on the list.
Each of your accounts are filled with their own informations:
(4) Label: A name or description of the account for convenience.
(5) Account Address: This is the public address you should give to the sender when you want to receive money in this account. In account #0, it starts with 4 and corresponds to the wallet's primary address. In the remaining accounts it corresponds to the account's first subaddress and therefore starts with 8.
(6) Balance: The account total balance. It cumulates the main address and all subaddresses for this account. Note: Subaddresses are managed in the Receive screen
(7) Edit Label: Click on this button to edit this account label.
(8) Copy Address to Clipboard: Click on this button to copy this account address to the clipboard.