You identify a pattern on our charts and want to go long 3 contracts on the SPX500 at 1960.50.
The margin required for the position is going to be 1960.5 x 3 / 200 (in the case of a 200:1 leverage) = 29.41 USD.
Five minutes before close, the market price is 1980.7 and you decide to take your profit rather than risk an overnight move against you.
The profit made on this position is 1980.7 - 1960.5 = 20.2 points.
With 3 contracts, each point is worth 30 USD, so the final profit is 20.2 x 30 = 606 USD.