Donwload the game here. That's where you'll get the most recent version.
Kerbal Space Program:: Download
The forum there also provides a quick way to interact with the developers, if you like the game I suggest you sign up.
"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
Unfortunately, some day is way the hell out in the future and you'll be destroying yourselves a whole lot. That's how the Kerbal Space Program works. Start the game. Run the tutorial and build a sensible rocket. After that you have no choice but to give in to your phallic compulsions and build ridiculous rockets and blow up your poor Kerbal Astronauts time and time again.
"What the hell are you talking about?" you ask? Like I said, start building rockets. Try to make it to escape velocity; try to make it to orbit; try to do anything and return the poor Kerman brothers to their home planet alive.
Here, we have a basic liftoff.
No, that solid rocket booster I'm using is not included with the game. Some guys on the Something Awful forums and others on the Kerbal Space Program forums have been making new parts. they're available here.
Index of /kerbal/mods Fortunately, the game's designers have made it easy to make your own parts with a little 3d modeling experience. You'll quickly learn which pieces are good and which aren't. If you're just starting, get Sunday Punch's pack and unzip it into your parts folder.
But back to the launch.
Notice how terrified Bill and Bob are? Bill and bob are damn wieners. Jebediah, on the other hand simply does not give a fuck. He will smile on through somersaults, losses of control, and sometimes even smile right up to the moment of his untimely death (which will happen frequently until you get in the habit of putting a parachute module on the ship.
But eventually, you'll get to orbit. At this point in development (version 0.8.4,) there are no missions, you have to make them for yourself. Go as high as possible, go as fast as possible. make the most circular orbit possible, make the most eccentric orbit possible without slingshotting past apokee (where Earth's apoapsis and periapsis are called "apogee" and "perigee," the corresponding points around the tentatively named "Kearth" are "apokee and perikee,) and achieving escape velocity
This is orbit
And
https://gist.github.com/1073201]This is a chart of circular orbit velocities and escape velocities when launching from "Kearth."
For fun: my 6 orbit/safe landing craft made before symmetry made it easy
And the ill-fated Colossus II design (broke up on ascent in upper atmosphere, killing all aboard.)
Just remember, when times get tough, look at jeb and smile. He's probably going to die, but he's right there smiling along with you.