Literal meaning, or the denotation, is the actual meaning of a word, the one you can find in a dictionary to explain what a particular word means. On the other hand, a symbolic, or connotative meaning, is abstract, and usually quite different from the word's literal meaning.
E.g. a dove is a type of a bird according to its literal meaning; however, it is a symbol for freedom and purity, according to its symbolic meaning.
Answer: The effects from 9/11 are mainly the lives lost and the spot where the twin towers used to be is now a small memorial spot with the names with everyone that died. There is also the fact that people have to go through that day every year.