Margin (M) represents the amount of money that you need in order to enter a trade.

Margin Level (ML) shows the ratio between your account’s Equity and Margin. ML = E/M *100

Free Margin (FM) tells you how much funds you have left to open new trades. FM = Margin – Equity

As a simple rule, if Equity = Margin, then Margin Level = 100% and Free Margin = 0 and therefore you will not be able to place new trades.

See more on Margin Requirements.