Possible hologram or photonic energy manipulation, reading nerve signals in the wearers body to determine what the wearer wants.

The objects created by the device can be physical, solid objects in the form of pseudo-matter that can be easily generated by compact factory modules but slowly disintegrate over time if not supplied by special energy from the factory or maintenance unit.
This kind of technology is sometimes used in missile launchers by vehicles and infantry that don't want to carry around heavy loads of ammo and choose to supply missiles from a central power source if needed.
The device of the picture is a very sophisticated variant of such a technology, seemingly beyond the understanding of the individuals of this species, at least who are known to be alive at the time of the picture.
It can create solid objects, such as the spear, that retains and regenerates its sharpness and integrity perfectly as long as the hand device is near, while having quite a light weight.
It might also have other functions, the individual in the picture probably has to figure that out on his own.

And also yes, the shapes and energy emissions created are influenced by the user's neural system and thus will.

Making constructs