Tool using and even tool manufacture are not activities unique to humans. Many creatures use naturally occurring materials to help them - thrushes drop snails onto stones to smash them, chimpanzees use straws to extract termites from their mounds - and sometimes they modify them - breaking off the desired length of straw, for instance. This requires a degree of forethought: visualizing the task's requirements and selecting an appropriate tool.
But early Homo carried this one stage further: they manufactured tools from stone. This demonstrates not only their physical skills (greatly enhanced by the development of an opposable thumb giving a precision grip) but also quite advanced conceptualization: visualizing the required tool and planning the necessary actions (the angle of striking blows to detach flakes, for instance) to produce it.
As time went on, the tools became more sophisticated, requiring increased manual dexterity and more advanced planning.
Later this controlled production of a designed tool was not enough; considerable effort also went into making the tool aesthetically pleasing. Such attention to appearance and feeling must indicate the stirrings of increasingly advanced intelligence and mental complexity.
