How to find domain and range of a parabola?

The domain is the value of x, the range is the value of y.
A parabola opens infinitely to the right and left, so x can be any number, the domain is all real numbers
Vertically, however, a parabola opens only one way, either upward or downward. when it opens upward from a a certain level, say, the lower point (the vertex) has a y coordinate of 2, we say the range is all real numbers larger than or equal to 2, or y≥2. When it opens downward, we say the range is all real numbers smaller or equal to 2, y≤2

Where are the functions?