The orb rests in Doctor Strange's Sanctum Sanctorum in a room called the Chamber of Shadows. It usually is inside a display case with three curved legs. When summoned, the glass covering rises from its enchanted Cask of Concealment and the ball levitates. Likely (though unconfirmed) to be completely of Agamotto's own creation, it is nonetheless directly empowered by him extra-dimensionally and is in some way connected to him.
While powerful, the Orb has been blocked by exceptionally powerful mystic forces, even those lesser in strength in terms of raw power compared to Agamotto (such as Umar of the Dark Dimension (whose power surpasses that of Doctor Strange and rivals that of Dormammu, Odin and Zeus) or the Enchantress of Asgard (who, while ranking among Asgard's top twenty magic practitioners, is reasonably less powerful than Umar) who do not want their exact location known.
Normally it is used for scrying. It will often match the appearance of Earth like a globe and point out possible dangers.
The Orb of Agamotto can be used to teleport others or to travel into Agamotto's personal realm.
The Orb was once thought destroyed when Doctor Strange's Mansion was heavily damaged, but Agamotto was able to preserve all of Strange's artifacts.
The Orb is also capable of projecting a telepathic voice (different to each who hears it, yet with the same essential meaning, likely from the ethereal Agamotto himself) after displaying an image in its depths of the desired subject, revealing the past of the Evil Eye of Avalon while simultaneously displaying corresponding images; as Doctor Strange had been expecting such a voice, it seems that either the Orb had displayed such an ability in the past, or the Sorcerer Supreme knew it was possessed such an ability.
The Orb can peer into other dimensions and other worlds, automatically detect and locate the use of powerful magic, and reveal any great evil threat to the world. Though it is possible to view images of other planets or outer space through the Orb in the same dimension, from Doctor Strange's inability to find Nighthawk thus makes it apparent that one must know the general location of the desired person, object or place, or else he would scour the cosmos for an eternity. The Orb is even capable of finding dead beings, at least those the user had been considerably familiar with.
The Orb can be used as a gateway for the viewer to enter into the dimensions it displays. It also seems to be dimensionally linked to the Eye of Agamotto. Individuals entering the Orb can at times exit through the Eye and vice versa.
In Other Media
The Orb of Agamotto appears in Thor as an easter egg for the fans. It is briefly seen in Odin's treasure room, alongside other prominent Marvel Universe artifacts such as the Casket of Ancient Winters and the Infinity Gauntlet.