The function you are referring to is the absolute value function, which is denoted as $f(x) = |x|$. The absolute value of a number is its distance from zero on the number line, without regard to direction.

To evaluate $f(-3)$:

$f(-3) = |-3| = 3$

So, $f(-3) = 3$.

Would you like further details on absolute value functions or have any other questions? Here are some related questions:

1. What is the graph of $f(x) = |x|$ like?
2. How does the absolute value function behave for positive values of $x$?
3. What are some properties of absolute value functions?
4. Can the absolute value function be expressed in piecewise form?
5. How do you solve equations involving absolute value?

Tip: Absolute value functions always yield non-negative outputs, regardless of whether the input is positive or negative.