When you plug your USB cable into the computer, it should recognize it. You will know if this works when you push any button and it shows a yellow light go on and off in the upper left hand corner. If it doesn't recognize it, go to Live, Preferences, click on MIDI Sync, and you should be able to find the LaunchPad on Control Surface. That should auto map it. Will post back soon to show how to map specific sounds to specific triggers.
We were trying to map parts of our midi controller to functions in Ableton and we figured out how as well. Actually there is one problem with Ryan's awesome answer. I believe the yellow light is in the upper right hand corner. Also we figured out how to manually map a midi controller. Here is a link to the help page on Ableton live where we found a video tutorial that taught us how to map a controller manually. https://www.ableton.com/en/help/
It still wouldn't sync up, so we looked into whether or not there is a driver for the launch pad. We went to the website for the device, and found the driver Novation USB driver 2.5. It worked!
Also we figured out how to manually map a midi controller. Here is a link to the help page on Ableton live where we found a video tutorial that taught us how to map a controller manually. https://www.ableton.com/en/help/