What do the different things in an equation mean?

Problem:

Napoleon fires a cannonball into the air. The height, h meters, of the cannonball above the horizontal ground, t seconds after launch is given by the equation.

h=-4t^2+15t+9

What does ax^2 mean? What does bx mean? What does c mean?

I'm supposed to find out what information is represented by the constant 9 in this context but I dont know what any of the information represented is?

Please help me.

Thank you so much.