To fully understand a symbol a reader should?

This is quite a broad question and may prove difficult to answer easily but here's an attempt. I will use an example, in Tennessee Williams "Sweet Bird of Youth" he looks at characters who were once young and beautiful and could rely on their looks and how they have now faded and no longer are able to do so. The most famous line of the play is a reference to "the enemy, time, in us all." Throughout the final Act a clock ticks in the background and this conveys the passing of time and that no matter what time will continue so look for references such as this. He also makes use of birds having them appear and then vanish and this also shows the nature of time and how it is fleeting. Through these symbols Williams conveys the simple message that time goes all too quickly and will continue to do so. All in all, to understand a symbol look to references, such as these, which appear throughout the play, novel, poem or short story, which you are studying. Hope this gives you a rough idea of how it works, any other queries about this example or the information given just post to my message board. Hope this helps.