If you don't know what Margin Trading is, simply don't do it & stick with the regular trading, sell only what you have in your pocket.
Margin Trading means you're Buying / Selling something you don't own, meaning the broker (exchange) will take huge part of your funds in front (as an escrow for the trade) depending on the leverage you're using, the more your leverage the more the Margin taking by the broker.

YES, it's profitable if things goes so good in your favor BUT it's also so bad the same way as good it is.