The Space Gem allows it's user to manipulate space in a nearly limitless manner when used properly. With limited knowledge, a user can teleport to any place in the universe with but a thought. Any persons or objects touched by the user can be moved as well. The gem can also change distance between objects in space, making the user appear to have super speed. The gem can also be used to pinpoint the location of a person or place.
With great knowledge of the gem (or in unison with the other Infinity Gems), the Space Gem can allow it's user to be omnipresent - simultaneously in every place in the universe.
Originally called the Soul Gems, the Infinity Gems were gathered by the Elders of the Universe to destroy Galactus. After their defeat, the Space Gem remained in the possession of the Runner, who did not know the gems purpose but was able to use it to travel faster than he ever could before (he was really warping distance in space, not traveling faster). The gem was taken from him by Thanos, who gathered all the gems to unite them in the Infinity Gauntlet.
Adam Warlock next possessed the Gauntlet, but gave the gems to individuals of his choosing for safe keeping. He chose Pip the Troll to guard the Space Gem as he had a natural ability (cowardice) to teleport from danger (and thus remove the gem from harm).Even after the gem was removed from his keeping, Pip retained the teleportation abilities bestowed by the gem, an obvious side effect of possession (although this may only be for long-term possession).
Wielders of the Power Gem
In Other Media
In the Marvel Cinematic Universe, the Space Stone is heavily hinted to be the Tesseract. The item is shown to be capable of opening portal through space, which allows the Chitauri to invade Earth during The Avengers.