The arm in question has two rotational degrees of freedom, and one translational degree of freedom.
To try the visualization tool out, you need to run the animate.py file with the proper libraries installed. (matplotlib 3.0.3 supported).
You can then use keyboard controls: use x, y, z to select axes (x axis, y axis, z axis), and then the up and down buttons to increment the position of the target coordinate. If you click 'r' on your keyboard, it will reset the position.
Based on the fantastic vis-tool for open-quadruped