The broker compares two numbers: your equity and your margin. This comparison in percent is called the margin level. Equity equal to the margin is 100%. Equity at half the margin is 50%.
Here’s an example of what not to do: a trade with your whole account. You have $1,000, you open a $10,000 trade with leverage of 10, and the whole account goes into margin. The price moves 3% against you from your entry: minus $300, equity $700, level 70%. The price moves 5% against you from your entry: equity $500, level 50%. In the simulator, this is where the stop-out happens: the trade closes on its own. Half the account is gone because the price moved 5%.