The bigger the value of the x2 coefficient (a), the steeper is the parabola:
You can see from the table and the graph that for every point from x=0 the y values of the blue function with a=1 are smaller than the y values of the orange function with a=2 and so on for the functions with a=3 and a=4. Bigger y values result in bigger distances from a straight line (a=0) and a steeper parabola.
The example is marked in red on the graphs and in the table. At the point x=2 the blue function with a=1 equals to f(x)=x²+3x-10=2²+3*2-10=4+6-10=0.
The orange function with a=2 equals to f(x)=2x²+3x-10=2*2²+3*2-10=8+6-10=4.
The grey function with a=3 equals to f(x)=3x²+3x-10=3*2²+3*2-10=12+6-10=8.
The yellow function with a=4 equals to f(x)=4x²+3x-10=4*2²+3*2-10=16+6-10=12.
What made the difference between the y values is 1*2² compared to 2*2² and so on.
The black arrow on the graph shows the distance between the y values of 0, 4, 8 and 12.