Help wanted. How does gravity work?

Guest here, can someone explain to me how gravity works. I'm trying to code a quick platformer game in C++, but my program isn't working the way I wanted it to. My programming is flawless (and by that I mean it does what I want it to do), the only problem is that I'm having it do something that bastardizes physics. As you can probably guess, I've never taken a physics class before.

Gravity is a force that moves objects down at a certain rate, but how does the ground cancel out that force? Does the ground also create a force that cancels out gravity's force? 

Also, how would you go about creating a gravity program?

>>3
You don't need to bother with any of that curvature of space time horseshit. You don't even need to bother with Newton's Law of Universal Gravitation. All you need to know is that gravity is a force that always pulls objects down. The magnitude of this force depends on the object's mass. When the net force on an object is not zero, it will accelerate or change velocity. (Newton's Second Law of Motion)

What exactly is a ground force? And how does it keep an equilibrium with gravity's force?
The "ground force" is a reaction to the force of the object hitting the ground. Object exerts force on ground --> ground exerts equal and opposite force on object. (Newton's Third Law of Motion)

An object resting on the ground will have the force of gravity pushing it downwards and a force from the ground of the same magnitude pushing it up. This is static equilibrium.

Collisions are trickier and I've wasted too much time on you already.