Balance is the amount on your account recorded taking into account all completed trades and transactions (trading, depositing, withdrawing of funds from the account).
In contrast, equity is the amount on the account, taking into account current open trades.
Margin is the amount on your account, which is blocked when you open any position (trade). It is like a kind of collateral for transactions.
Leverage is the ratio of the amount of the base currency of a contract to the equity required to open a pledge position (see the term “Margin”). For example, a 1:100 leverage means that EUR/USD contract of 1 lot (€100,000) requires 100,000/100 = €1,000 of collateral (provided that the deposit is in EUR).
If the deposit is in USD, that is, the base currency of the pair differs from the deposit currency, then the base currency must be converted into the deposit currency at the rate in existence at the time of opening the trade. That is if the deposit is in USD, and the margin is in EUR, then €1,000 * exchange rate (at the time the trade was opened) = margin in USD (in the deposit currency).