Writers use symbolism because it gets across deeper and richer meaning in fewer words. Take a look at these examples.
Let's say that you're reading a story about a guy named Frank. In the story, Frank leans against a brick wall as he's waiting for his dad to show up.
Does the brick wall symbolize (stand for) a bigger idea or concept?
Not really? Well...
What if you found out that Frank has been trying to find a job for six months, but nobody will give him a chance because he's an ex-convict? Now that you know that, think about the brick wall. Is it possible that it's symbolic of (that it symbolizes) his inability to get a job and move forward with his life?
Can you see that the simple thing (a brick wall) might be a symbol for a bigger idea (blocked goals, an obstacle, or a barrier to progress)? If you can see that, then you realize that the brick wall is a symbol for something else, especially if brick walls show up over and over again in the story.
Here's another example:
Let's say that you read a story about a man sitting in a green chair while playing with his new baby. Later in the story, another character saw a cat with kittens, partially hidden under a branch filled with beautiful green leaves.
As you continue reading the story, you notice that the color green is mentioned by the author every time there's a scene that has to do with the beginning of life, like a scene with a baby or a kitten.
So what does this mean? It probably means that in that story, the color green is a symbol for the beginning of life, or rebirth, or the cycle of life, or something like that.
So why do writers do this? (Filmmakers do the same thing.) Writers do this because it lets them put across deeper, richer meaning in fewer words. You see, in the story about the man and the baby and the cat with her kittens, the author wanted the concept of the creation of life to be bigger than just the baby and the kittens; the author wanted it to be all over the story, infusing the story with a sense of life.
So rather than write many sentences about how life seem to be all over the place in the story, and that it was in the air, and in the trees, and in the ground, and everywhere, the author just use the color green to symbolize the creation of life. It makes the story more beautiful and more artistic.
Symbolism is really an artistic expression that can be open to interpretation. Some symbols are clear and easily understandable (like a wedding ring being a symbol of love), and some can be interpreted differently (like a waterfall in a story about a man's struggle with his father's alcoholism). You might have a different opinion from somebody else about a symbol in a story. If you do, that's good! It means that you can have an interesting discussion about the story (or the movie) and what it means to you.
The free, downloadable printable guide (above) gives more examples of symbolism, along with color pictures. It also shows you a step-by-step procedure of how to identify symbolism in a sample story, and the relationship between symbolism and metaphor. Print it, do the assessment, and you'll be on your way to being an expert on symbolism!