The steel wire is held in a appartus so it is horizonatal. A string is attached to the edge of the circular drum and passed along its side. A mass is then hung from the string. The mass pulls on the string which pulls on the drum applying a torque to the steel wire. This torque can be seen as a needle is attached to the steel wire so that it is pointing straight up. A scale is placed behind the needle so that the needle is pointing at the zero. When a torque is applied to the steel wire the steel wire twists causing the needle to move with the wire. The angle of twist at that poont on the wore can be read from where the needle is now pointing on the scale.  

You can try a very similar experiment virtually here: Rigidity Modulus of The Suspension Wire of A Torsion Pendulum

In the second part of this experiment the steel bar is suspended vertically. It is fixed at the top point. In this set-up a wooden circular drum used and is attached at the bottom. Attached to the other side of the drum is a sensor that can detect the circular drum twisting. The drum is given a push cauing the circular drum to twist in one direction and then twist back in thw other direction, similar to a pendulum swinging back and forth. These oscillations are read by the senosr and displayed on the screen.  

While it uses a different method to measure oscillations the equations used in this experiment are explained well in this guide.

You can try this experiment virtually here: Moment of inertia of a Torsion Pendulum