How to move a object in relation to relative rotation

How do I move an object in the direction it is facing no matter where it is facing?

I am making an airplane, and I need it to move in the direction I am looking.

You can do that with transform.forward:

this.gameObject.transform.position += transform.forward * Time.deltaTime * movementSpeed;

this.gameObject.transform.position += transform.forward * Time.deltaTime * movementSpeed;

If You use physics, try this:

public float speed;
public Rigidbody rb;

private void FixedUpdate()
{
     rb.velocity = transform.forward * speed;
}

Or You can change position directly without physics:

public float speed;

private void Update()
{
     transform.Translate(transform.forward * speed * Time.deltaTime);
}

Check if your object with the movement script has blue arrow (Z-axis) in the direction correct direction.