Symbols, as such, represent ideas. They can be abstract ideas, so in a sense they can simplify. But, they also can be used to describe things hard to express, or things not fully known. They can also have several meanings.
A sun, for example, can symbolize the day, but it can also mean life and lots more. Symbols are means to express, and we should understand they have great influence on us.
It can be everything, a picture, a person (e.g. Martin Luther King), a sound (soundtracks can also represent something, can’t they?), an object, and lots more.