Mechanization refers to the use of powered machinery to help a human operator in some task. The use of hand powered tools is not an example of mechanization.
The term is most often used in industry. The addition of powered machine tools, such as the steam powered lathe dramatically reduced the amount of time needed to carry out various tasks, and improves productivity. Today very little construction of any sort is carried out with hand tools.
The term is also used in the military. Here it refers to the use of vehicles, notably APCs, to move troops that would otherwise have marched into combat. Mechanization dramatically improved the mobility of infantry, and today what little infantry is not mechanized is airborne.