SSIS Script Task Read And Write Variables - 2

In this Video we will look into how to read a value from a variable and how to update a value of Variable

[EdwinCloud]

how do you show the variables tab in the first place?....

[trdrhyme]

In Script task, how can I use a Project variable being assign to a ReadWriteVariables property in the Expression? i would like to write a value to a Project variable from the Script Task.