What required margin is
Margin is the amount your broker locks as collateral to open a trade — not a fee. It returns to your free balance when the position closes. Required margin = (trade size × unit price) ÷ leverage, so at 1:100 a 100,000-unit standard lot locks about 1,000 units of the base currency.
Leverage enlarges the position you can open with a small balance, but losses are still calculated on the full position. Treat leverage as financing, not as a profit multiplier: it scales gains and losses by exactly the same factor.
