Reading the toolbox strip
At the bottom of MT5's Trade tab you will see a line like this:
Balance: 1,000.00 Equity: 962.40 Margin: 43.40 Free margin: 919.00 Margin level: 2,217%Each number answers a different question.
Balance
What the account would show if every position closed at the price it opened. It changes only when a position is closed, or when you deposit or withdraw. Balance is history; it tells you nothing about the trades open right now.
Equity
Balance plus the floating result of open positions. In the strip above, open trades are 37.60 USD under water, so equity is 962.40. This is your real account value at this moment, and it is the number the stop out rule looks at.
Margin and free margin
Margin is the collateral locked by open positions. Free margin is equity minus that: what remains to open new positions and to absorb losses.
free margin = equity − margin
Margin level
margin level = equity ÷ margin × 100
A healthy account runs at several hundred percent or more. When it approaches the stop-out level for your account type, the platform begins closing positions.
Summary
Balance is closed history, equity is what you have now, free margin is what you can still risk, and margin level is the number that decides when the platform steps in.