The FootstepSounds component is intended to be more of an example script than anything, because it shows one possible way you can add footstep sounds. As such, it is commented throughout, and you can read how it works by opening the script file.
But basically, you add a new Sound child to your character, and add the component to the character's root. Then assign however many footstep sounds you want in the AudioClip array, and assign the new Sound child component as the Sound To Play From field.
To play the sounds, you then need to create Animation Events (a Unity feature) within your walk/run animations. These events should call the FootstepSounds component's PlayFootstep function, which will play one of the AudioClips you've provided at random.
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But basically, you add a new Sound child to your character, and add the component to the character's root. Then assign however many footstep sounds you want in the AudioClip array, and assign the new Sound child component as the Sound To Play From field.
To play the sounds, you then need to create Animation Events (a Unity feature) within your walk/run animations. These events should call the FootstepSounds component's PlayFootstep function, which will play one of the AudioClips you've provided at random.
Worked for me!