CODE EXAMPLE FOR CSHARP

unity 3d camera rotate up and down

public class CamRot : MonoBehaviour
{
    public float rotationSpeed = 50;

    void Update()
    {
        Vector3 rotation = transform.eulerAngles;

        rotation.x -= Input.GetAxis("Mouse Y") * rotationSpeed * Time.deltaTime;

        transform.eulerAngles = rotation;
    }
}