Equity is a current amount of funds in an account including the present financial results of the opened orders. I.e. it is the sum that will be on the balance sheet when all orders are closed at the present quotes. Equity changes dynamically depending on gains and losses on opened orders.
Equity equals Balance plus the current financial result of the opened orders.
When you have no opened orders in an account, the values of Balance and Equity are equal. If there are opened orders in your account with the current financial result of $1500, then Equity will equal the Balance plus $1500. If your orders closed with $1500 of loss, then Equity is Balance minus $1500.