Give it a name here call it what ever you would like.  Then press save.  Next press the blue disclosure button indicated by the red circle below.

    This will bring up the data entry menus.   Here is a sample weekly credit strangle using a short call spread selling the 1375 and buying the 1400 strike price.  For more help  on data entry please see manual here.

    Once the data is entered its time to view the spread.  Press the magnifying glass from the portfolio menu after selecting the spread you wish to view. 

    This last entry is where we set volatility, interest rate and the chart bounds.   Use the volatility calculator found here to get a volatility value for the chart.

    Notice for this spread I changed the bottom bounds to 1300 to accommodate the current price being lower than the auto generated values.  Often times you want to see values that are not near the range of the strike price.  Pressing render gives the results below.

    One thing to note here this spread was a credit spread and the negative value indicates a credit.