The document provides information on writing variable expressions to represent word phrases and vice versa. It defines commonly used variables like x and y as placeholders that represent unknown numbers. It provides examples of translating phrases like "four more than a number" to the expression x+4 and translating expressions like 3(x+10) back to word phrases. The document emphasizes that variables help solve real-world problems by breaking them into steps. It includes an example of writing an expression for the total earnings from candle sales based on the number of scented and unscented candles sold.