1. The problem is to simplify and understand the function $y = \sqrt{x^2 - 4x + 4}$.\n\n2. First, recognize that the expression inside the square root is a quadratic trinomial. We try to factor it: $$x^2 - 4x + 4 = (x - 2)^2.$$\n\n3. So the function becomes: $$y = \sqrt{(x - 2)^2}.$$\n\n4. The square root of a square is the absolute value, so: $$y = |x - 2|.$$\n\n5. This means the function outputs the distance of $x$ from 2 on the number line.\n\n6. The graph of $y = |x - 2|$ is a V-shaped graph with vertex at $(2,0)$, opening upwards.\n\nFinal answer: $$y = |x - 2|.$$