Let us start with the easiest way.
Click on “Buy”. Be aware that the “Sell” box does have the same settings. So we will explain one only.

Pos: on the top shows if there are previous Open positions or not, how many, and in which direction.
Example : If there is a Short or Buy position Open, it shows +1. If you had 2 it would show +2. If it was a Long position it would show -1 or -2. So Short is +, and Long is -.

Type : In that box, are listed all the possibilities you may trade.

Opening a Position :
You have 2 choices available to click on : Market or MIT (Market if Touch).
Both are the market value at which you wish to buy. You may use either one.
Market : is the fastest way to Buy at the present Market value.
MIT : you have to define in the window called “Details”, at what value you wish to Buy when the market reaches that value.

Details :
There you specify the number of Lots. The minimum of course is one lot. Click on the arrows on the right side to define you choice.

Be aware that the value you specify in that “Lots” selection means that this value will be multiplied by the amount of money required for the Margin amount of that Contract and will be deducted from your portfolio.
Example : Assuming S&P Margin amount for Overnight trading is US$4,000, if you specify 1 lot, that amount will be deducted from your portfolio. If you specify 5 Lots, 5 times the margin will be deducted. So if upon placing that order you get an error message relative to Margin call, it is because the number of lost is greater than you can afford.

The box below is the Market value at the present moment for that Contract.

To be continued.