The Balance is the total financial result of all fully executed transactions on a trading account. That includes deposits, withdrawals to and from the account, fees for opening trades which are deducted directly from the account Balance (e.g. commissions) and the Realized P/L of all closed positions.
The Live P/L of any open positions does not affect the Balance while those positions are still open. The Balance will be recalculated once those positions close.
For example, if you deposit $10,000 in a new account and you open a trade that wins $200 (live P/L = $200). While the trade is still open the Balance remainss at $10,000. If you close the trade while winning $200, your Live P/L will become $0 and your Balance will increase to $10,200.