The Allegory of the Cave
There are several symbols used in the allegory of the cave: the cave, the prisoners, the shadows, the puppets, the jagged path and the sun.
The purpose of the allegory of the caves is to tells us that our opinions and experience of the world comes from our senses, however real knowledge can only come from knowledge of the forms.
We can gain knowledge of the physical world, however this is constantly changing and is purely opinion.
Plato believes that our experience of the world, is only a imitation of the true forms which exist in the abstract world of the world of the forms. We experience particulars, however they are a fleeting and changing example of the true form. For example, experiencing a tree, or an act of love, is a particular, or an example of the form of a tree, or a form of love.
Look at all these different examples around me, they all appear difference, but share some similar qualities: they have trunks, branches and leaves. They all possess tree-ness and are all poor imitations of the perfect form of tree.
A philosopher
There is an essential form, which is the form of the good.
The form of the good allows other things to be known. It is by knowing this form, that we can behave in a moral or just way. Things are good if they are filled with goodness and clear reflections. The form of the good is like a light and illuminates everything else.