How does gravity work?
Sorta like this.
Take a pop can. I've got one near my desk, and if you don't...drink more pop. Or something. What we want is a middling sized object.
This object has mass. Now, everything in the /entire universe/ strives to become bigger. Whether this is because bigger things are totally awesome, God does it, or it's simply the random law of physics that happened when the big bang happened--everything tries to become bigger. Bacteria try to become more advanced bacteria, kittens grow into cats, small fellows with cylindrical heads roll Katamaris for larger men with cylindrical head to make stars and planets out of. Everything /wants/ to become bigger, and this one does it through the property that mass attracts other mass.
Gravity is an extension of the strong nuclear force. Your math gets a little futzed when you try to apply the EXACT same equations, but that's why physics professors are still working on the theory of everything. Atoms pull each other together, this is why everything is not constantly exploding violently. (The weak nuclear force is what constantly pushes the atoms apart, keeping everything from supercompressing. It's really /about/ as strong as the strong nuclear force, it's a misnomer.)
Therefore, what you're holding, in addition to being mass, is also a giant pile of atoms. (Multifunction!)
A bunch of atoms, working together however intentionally or unintentionally, want more atoms sticking to them. This is gravity.
However, the problem is that atoms are frankly frigging small. If you hold two magnets down (Which work more on alignment of atoms than the other thing, which is complicated and unrelated, frankly.), they're not going to slam together. Two pop cans will take /billions of years/ to touch, because the earth is busy trying to make them a part of its mass.
Now, let's take a vacuum. Not outer space. Outer space ain't a vacuum of gravity, there is gravity frigging /everywhere/. It's just that it's pulling you in a lot of different directions, and the end result is you're not being /especially/ pulled anywhere. You're not pulled apart cause it's pretty weak in space compared to standing on the earth. A species born and evolved in space would go down to earth and be like 'wtf I'm freaking HEAVY'.
But no, we want a completely empty universe with our laws. Maybe our King of All Cosmos can get drunk and knock it all out of the sky again. He does that once in a while.
Let's put in our two pop cans.
It may take no time at all. It may take a fair chunk of time, I don't know what equations you use for this, but no matter how far away you put those pop cans, they will eventually touch. (Assuming you yourself are breaking the laws and don't have gravity, otherwise since you're bigger than a pop can, they will eventually touch YOU. And since you're the only thing in the universe besides the assailants, you can't claim harassment for it. Sorry.)
Now, we fast forward to the universe. We had no crap, then suddenly we had a lot of crap, everywhere. It didn't become a huge ball only because the speed at which everything was moving was considerably faster than the speed at which the mass was clinging together. Eventually, however, everything started clinging together, in generally round shapes. (Incidentally, the earth is not perfectly round in RE theory. It is actually /very/ slightly pearshaped.)
Inertia says that this stuff isn't gonna stop moving till someone stops it. Now we move to our next point: Why, if gravity works this way, isn't the universe slowly crunching as masses are pulled together?
This is because if you move at the exact right speed, you ignore gravity.
How is it remotely possible that everything in the universe is moving at the exact right speed?
A lot of it isn't. A lot of it is eventually going to crash into other stuff, or already has crashed into other stuff, or is crashing RIGHT NOW. The earth is moving at the exact right speed, because if it's a one in a million chance that something will go right, if you roll the dice a nigh-infinite amount of times, you're gonna get it a fair chunk. (Well, nigh-infinitely, but there aren't really enough zeroes for something that isn't quite infinity.)
Another way you could do this is water. Yeah, stuff in water tends to float together eventually, given no currents, or eddies. Try your bathtub and light stuff. This produces a disk shape, roughly
Now, imagine two planes superimposed upon each other perpendicularly, with a layer of water with things floating on 'em. You'd get a sorta shape like star fruit.
Now, imagine three hundred and sixty planes superimposed upon each other a degree apart, with a separate layer of water. You get a roughly round shape.
This, highly, highly simplified, is how gravity works.