In the equation $y = ax^2 + bx + c$ of a parabola, what do "$a$", "$b$", "$c$" represent? I have trouble grasping some basic things about parabolas. (This should be easily found on Google, but for some reason I couldn't find an answer that helped me).
I know one simple standard equation for a parabola:

$$y = ax^2 + bx + c$$
My problem is: I'm not sure what the following letters represent: $a$, $b$, and $c$.

Please try to explain to me what each of these letters represent in the equation, in a simple manner so I will understand, since I have very basic knowledge in math.
Thank you

You can use an DGS to get an idea. I created a worksheet for you:
Use your mouse to change the numbers on the slider and see what happen. To get smaller steps use the left mouse button to active the slider and then use left- or right-arrow on you keyboard.
http://www.geogebratube.org/student/m69762
