What does the author mean by “ symbol “.?

it really depends because they could be doing quotations around like a paragraph. so it depends on what you're asking because if you're asking for the definition then it means a Mark or character by used as a conventional representation of an object function or process it stated in the dictionary if you want to double-check.

- "when these words are put together to convey a meaning it is known as a sentence. a sentence is a group of words that makes complete sense. placing of words in a sentence is very important. the second sentence is a question."

b. our party quickly made its way into the cave / but we failed to find our host [the cyclops] himself inside.