If you have an quadratic equation 
and you want to grab this equation. All you do is draw the reflection of the graph that is folding in x-line. for example if $latex y=x^2, and you want to draw the equation of y=|x^2|, you just do nothing. Because the negative part is non-exist. Although, if you get y=x^2 – 2, you have to fold the negative part to the top. It makes the equation to make absolute value equation. One thing that make The Whole point possible is by putting the equation to folded y=0 so no negative value will be shown.