Random Position For GameObject

Well, I agree the question is kind of broad and vague, but should not have been closed and considered off topic. Have a look at Random.Range, and use it for each axis on a Vector3. Say all your "notes" will be on the same Y position, but x and z will be random, just for example's sake.

 float x;
 float y;
 float z;
 Vector3 pos;

 void Start()
 {
     x = Random.Range(-25, 26);
     y = 5;
     z = Random.Range(-25, 26);
     pos = new Vector3(x, y, z);
     transform.position = pos;
 }