Consider the quadratic function $f(x) = A(x-h)^2 + k$. This is studied extensively with its parabolic graph in most texts.
We will examine mapping diagrams for an alternative visualization of  the key features of $f$.

In considering the quadratic functions in this form, we can read the instructions for the function as a composition of commands:
1. Subtract $h$ to $x$ to form $x-h$.
2. Square the result of step 1 to form $(x-h)^2$.
3. Multiply the result of step 2 by the magnification factor $A$ to form $A(x-h)^2$.
4. Add $k$ to the result of step 3 to form the quadratic function $f(x) = A(x-h)^2 + k$

Note that for Example QF.0, $x^2-2x-3 = (x-1)^2 -4$ so $A=1$, $h=1$ and $k = -4$.
You should  review Example QF.0  to explore for yourself how the numbers $A$, $h$,  and $k$ are realized in the features of the mapping diagram.

Before further discussion we'll examine some simple and important examples.

Example QF.1.1 : $q(x) = x^2$.  " Square x" : $x^2$  The core quadratic function.
Example QF.1.2 : $q(x) = x^2+ 2$.  "Added value after $x^2$ ": $2$
Example QF.1.3 : $q(x) = (x-2)^2$.  "Added value before $(...)^2$ ": $x - 2$
Example QF.1.4 : $q(x) = 2x^2$.    "Constant multiple": $2$

Now that you've looked a some simple examples here are four more [important] examples for the quadratic function $q(x) = Ax^2$.
These examples illustrate the effect of  the quadratic coefficient, $A$. Compare the mapping diagram with the graph.

Example QF.2.1 : $A =-2; q(x) = -2x^2$
Example QF.2.2 : $A = 2; q(x) = 2x^2$
Example QF.2.3 : $A =\frac 1 2 ; q(x) = \frac 1 2x^2$
Example QF.2.4 : $A = -\frac 1 2; q(x) = -\frac 1 2x^2$

You can consider the effect of other adding "values after $x^2$ "in the exercises or with the dynamic Example QF.DV.0.
"Adding value before $(...)^2$ " is worth a few more examples treated as compositions of $g(x) =x - h$ before $f(x) = x^2$
Example QF.3.1 : $h =2; q(x) = (x-2)^2$
Example QF.3.2 : $h = -2; q(x) = (x+2)^2$

From this construction and understanding of the core quadratic function  $q(x) = x^2$, the following fundamental observations should make sense in the mapping diagrams:
• Extreme Value of $f$: The extreme value for $f$ will occur at $x=h$. This value will be $f(h) = A(h-h)^2 +k = k$.
• When $A \gt 0$ the value at $x=h$, that is, $k$ will be the smallest (minimum) value for $f$.
• When $A < 0$ the value at $x=h$,  that is, $k$ will be the largest (maximum) value for $f$.
• Magnification, The effect of $A$:  The value of $A$ can be seen by looking at the change in the value of $f$ from $x=h$ to $x= h+1$. $f(h) = k$ while $f(h+1) = A +k$. Though this change is not a constant for all changes in $x$, it indicates the magnification that will effect all other changes for $f$ from the core function of $x^2$. It will be greater for greater values of $|A|$, and will determine  whether it is an increase of decrease by whether $A \gt 0$ or $A < 0$. On the graph this is usually described as controlling the bowl shape of the parabolic graph of $f$.
• Symmetry of $f$ with respect to $x=h$: The values $f$ at $x=h+a$ and $x=h-a$ will be equal since $((h+a)-h)^2 + k= a^2+k =(-a)^2 +k =((h-a)-h)^2$ +k.
Thus $f$ takes on equal values for numbers symmetrically located by either adding/subtracting the same number to/from $h$ in the domain.

You can use the next dynamic example to see the effects of the quadratic coefficient and adding constants before and after $x^2$ simultaneously on a mapping diagram and a graph.

Example QF.DV.0 Dynamic Visualization for Quadratic Functions: Graphs and Mapping Diagrams