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?

>>21
>What exactly do you mean here?
Disregard that. Your first sentence answered my question.

Thanks to the help I received in this thread, my platformer engine is now working. But it still needs a little more tweaking before it can be used to handle some of the stuff I plan on throwing at it. It's amazing how the progress of said platformer is directly correlated to my understanding of physics. If I wasn't such a masochist I would have suspended this project and caught up on my physics lessons.

On a semi-unrelated note, programming things is a lonely endeavor. Thank god for the Internet.