ini baru level form 4 during my days.

should be switched to level form 1-3 by today's syllabus.

dude borrow money to gamble on stock market, stock market go down, banks liquidate his holdings (margin call) to avoid losing money, market sold off even more.

moral of the story, don't borrow other people's money to gamble.

Let's say you got $10, they let you borrow $100 to buy stock out of the $10 you have, so 1:10 leverage.
You use all $100 to buy in a stock, now the stock drop 25% due to dilution, so they ask you to come out with $25 in cash to cover the losses, you don't have the money to pay back so they have to sell all in the market to recover money and you still owe them for the outstanding amount.

Then can cover, nothing happens, you still hold the stock.

technically, no. It isn't even a loan.

Margin call is just additional & available funds that sits inside your broker trading account.

Think of it as a credit card. The money is there for you to spend to buy more stocks. But one rule, you must have at least remaining 40% balance at all times.

If you don't have 40%, then you are required to top up with money of your own until it goes to 40%. Otherwise, the broker will liquidate your stock position to reach back to 40% of available balance.