You think the price of gold is going to appreciate over the next few hours. You buy 100 oz, or 1 lot, of XAU/USD at the price of USD1,184.60. One lot is 100 oz x USD1,184.60 = USD118,460 (or USD100 for every USD1 movement in the price of gold).
Gold is trading at USD1,189.70 later that day, and you decide to sell. Your profit on the trade is USD510.00 (USD1,189.70 closing price - USD1,184.60 opening price x 100 oz).
Using leverage of 200:1, your initial margin would have been 100 oz x USD1,184.60 x 1 lot / 200 = USD592.30.