The Stone age was the early term used to describe the beginning time when humans, or our distant ancestors, began to use stone as tools. It is then furthered into two more periods of time known as the Bronze age and the Iron age respectively. All these ages were meant to convey when we began using certain tools in the genus homo, Stone age for stone tools, Bronze age for the advent of metallurgy, and Iron age for the period of time when we first started manipulating iron and steel.
However, in more recent years with the increase in the archaeological record, these common-use terms no longer have such a linear progression. The Ages have since been refined into new time periods known as the Pleistocene epoch, the Holocene epoch, and the Historical Record (the time period when written accounts took place). The Stone age is covered mostly within the Paleolithic epoch.
The Stone Age technically began in the Paleolithic Period during the Pleistocene epoch almost 2.6mya (million years ago) stretching to the beginning of agriculture 12,000 years ago. The Paleolithic period is further subdivided into 3 time periods; The Lower Paleolithic, Middle Paleolithic, and the Upper Paleolithic respectively.
LOWER PALEOLITHIC (or the first stage of the Old Stone Age)
The Lower Paleolithic industry is marked by the first use of stone tools by hominids. Homo habilis was the first discovered to be using tools to cleave meat off bone, as well as break the bone to extract the marrow. This marks a period where we get away from our Australopithecene roots of being mainly omnivorous, to becoming early carnivores. The first example of these tools is known as the Olduwan tradition, and involved mostly the hammering and flaking of stone to create a tool. The Olduwan tradition actually marks the beginning of the archaelogical record, as this is the point where we first begin seeing widespread tool use in the hominids.
The other aspect to the Lower Paleolithic is known as the Acheulean, and are mostly associated with homo erectus and begin around 1.8mya. It is typically noted that this period is also when we left Africa to populate Eurasia, as most often Acheulean tool use is seen throughout Europe and Asia, where Olduwan is limited only to Africa.
MIDDLE PALEOLITHIC (the second stage of the Old Stone Age)
The Middle Paleolithic, or Middle Stone Age, spans from around 300,000 years ago to 30,000, and is marked by homo neanderthalensis(Neanderthals) and anatomically modern humans developing (homo sapiens). Tools use is often shown to be more complex as Acheulean techniques due to a prepared core technique. This technique involved first preparing a stone to the shape you wished then modifying it further to produce the product you wanted. The time period also shows evidence of the first use of projectile weapons by the Neanderthals. Anatomically Modern Humans don't enter the picture until around 195,000 years ago, and there is a lot of evidence to suggest we may have mingled with Neaderthals on the landscape.
UPPER PALEOLITHIC (the last stage of the Old Stone Age)
This time period is marked mainly from our evolution in tool use from hand-axes and stones, to complex blade shapes. It lasts from about 40,000 years ago to 11,000 years ago. Modern humans, which evolved around 195,000 years ago, took the stage here and probably were one of the reasons for the disappearance of the Neanderthals. Many theories surround why this may have happened. This period also shows some of the first evidence of campsites, although it's debated that fire may have been an invention from the Lower Paleolithic. Artistic endeavors also compounded this era, such as cave and mobile art. This period shows the beginning of human creativity and ingenuity.
So even though the term Stone Age is still used, it makes it easier for archaeologists to separate it into three categories known as the Upper, Middle, and Lower Paleolithic Era's. There is some debate recently that may push tool use back even before hominids and into the australopithecene realm, which may cause these Era's to further be transformed.