1. **State the problem:** Factor the expression $x^2 - 4$. 2. **Important rule:** When you see something like $a^2 - b^2$, it can be factored as $(a - b)(a + b)$. 3. **Identify parts:** Here, $x^2$ is $a^2$ and $4$ is $2^2$, so $a = x$ and $b = 2$. 4. **Factor:** Using the rule, $x^2 - 4 = (x - 2)(x + 2)$. 5. **Explanation:** This means $x^2 - 4$ breaks down into two simpler parts multiplied together. 6. **Final answer:** $x^2 - 4 = (x - 2)(x + 2)$