1. **State the problem:** Evaluate the expression $y^2 - 5$ when $y = 3$. 2. **Recall the formula and order of operations:** The expression is $y^2 - 5$. According to PEMDAS (Parentheses, Exponents, Multiplication and Division, Addition and Subtraction), we first calculate the exponent before subtraction. 3. **Substitute the value:** Replace $y$ with 3 in the expression: $$3^2 - 5$$ 4. **Calculate the exponent:** $$3^2 = 9$$ 5. **Perform the subtraction:** $$9 - 5 = 4$$ 6. **Final answer:** The value of the expression when $y=3$ is $4$.