I have seen one tutorial where in Text property there is option to define the Variable. I would like to make the digital clock using that tutorial. Where can I find the "var" option to define the variable name?
That option only exists for AS2 and AS1, so you would need to set your Publish Settings for either of those for the variable element to be available for a textfield.
Using that feature can be problematic, so it is better to just use the text property of the textfield to read and assign values for the textfield.