Rotate GameObject on Axis

using UnityEngine;

public class RotateOnAxis : MonoBehaviour
{
[Tooltip("Applies a rotation of eulerAngles.z degrees around the z-axis, eulerAngles.x degrees around the x-axis, and eulerAngles.y degrees around the y-axis (in that order).")]
public Vector3 rotationSpeed;
//public float speed;
void Update()
{
transform.Rotate(rotationSpeed);
//transform.Rotate(Vector3.up * speed * Time.deltaTime);
}
}