Scripting Walking Sound Help?

Hey All ! I am working on a school project but I am an art focused student, so bare with me.

I have this script to play footsteps when our character walks:

 public class Walking : MonoBehaviour {
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
         if ( Input.GetButton( "Horizontal" ) || Input.GetButton( "Vertical" ) )
             audio.Play();
         else if ( !Input.GetButton( "Horizontal" ) && !Input.GetButton( "Vertical" ) && audio.isPlaying )
             audio.Stop(); // or Pause()
 
     }
 }

I have quite a few questions:

1)It works just fine, however we are using a controller for our game and this only works with the keyboard. I tried GetAxis but that doesn't work.

2) She still has the walking sound when she is jumping in the air. I have seen things about isGrounded, but I haven't found anything in depth enough on an explanation, so I don't understand how to add it to this code.

3) I might need to change the code so that a different noise will play when the character jumps and does other actions, so I have to know how to call on specific audio sounds. Would I do this playing the PlayOneShot (filename here)?

Thank you for any help! Again, I apologize that I am not one versed in codes and scripts.