Parts(mechanical or Electrical) used in articulated robot

I'd recommend buying a Lego Mindstorms NXT robot. By building and programming a robot, you will get a feel for the various pieces involved in a generic sense. Then, explore further by searching the web for industrial robots and control systems.

In industry, robots include all the elements of any industrial system: motors, linear actuators of all types, sensors of virtually any imaginable type, gearboxes, transmissions, pulley drives, ball joints, hinges, graspers, etc, etc.

If you build a small robot, like the NXT, and then imagine what you might want to accomplish with a larger robot, then you can do a purposeful search for the components you will need to accomplish your desired task. That will make the learning more meaningful than simply reading through a data dump about all the thousands of components that can be included in a robot.