What Are Simple Machines?
In today's world we are surrounded by a bewildering amount of machines, most of which seem magical. However all of them are made of the same simple machines. Simple Machines are just tools in the simplest definition. Now you ask what tools are. Well a tool is something that reduces the amount of work you have to do to accomplish something. There are six simple machines they are the lever, wheel and axle, inclined plane, wedge, pulley, and screw.
What Are Complex Machines?
Complex machines are machines that are made from several simple machines put together. For example a hedge trimmer is made of two wedges and lever. When you push squeeze the handles together, the blades (wedges) come together and cut whatever is in between them, if the material being cut is weaker.
What Are Robots?
Most People believe that a robot is different from a complex machine. It is in a way, but not really, the difference between a complex machine and robot is that a robot has a circuit board to help it "think". For example when you start a complex machine, it will continue to do the job it was set to do, until you stop it, it runs out of resources, or it breaks. However a robot can decide (after programming) when to perform a specific action at a specific moment in time.