I think Geogebra can handle a particular case for your question on demonstrating the shifting effect.
For the s/w to have something to plot, we give it a sample curve like $h(x) = x^2 - x - 12$.
Next, we ask the s/w to plot y = h(x - 2), where 2 is just particular value for t. The result clearly shows the resultant curve is just a right shift of the original by 2 units.
Plotting y = h(x + 2) is a left shift of the original.
Solving h(x - t) = h (x + t) is to find the point of intersection of the plotted curves.
Since the original quadratic is symmetric (with x = $-b \over {2a}$ being the axis), the two plotted curves are just displaced right and left of the same amount. They will meet at x = $-b \over {2a}$