The SpaceX company successfully launched its cargo to the Space Station. But they had another goal in mind and that was to see if, once the cargo capsule had peeled away, they could land the Falcon 9 booster rocket onto a floating barge because that would enable them to reuse the booster and provide a huge savings.
The idea was to have booster rockets slow its descent and then land it vertically on four legs. Alas, they got really close to success but not quite. Still, when you see the video of the landing, what they achieved was pretty impressive, since landing a 14-story high tower-like object and keeping it vertical is an enormous challenge. They got the booster to land exactly on target but failed to keep it upright. They came so close to pulling it off this time that it seems like they should be able to do it successfully within the next couple of attempts.