How to properly make a rocket controller.

I found some code on a youtube video, and after learning some stuff about c# I modified it and got some of it working, the 2 main things I don't think are working are applying thrust where the top of the rocket is pointing after I turn it, and also how to rotate the rocket on the x and z rotation axis. I sorta have this working but when I let go of the key it does not stop rotating, I want it to fall, I just want it to immediately stop rotating when I let go of the key. (I don't want to post a lot of stuff on here so I'm also going to ask 1 more question for something later into the game) It is a 3d game and I want it do something when you touch all four landing legs on the ground. I don't really know how I would do that. Here is my current code.

 using UnityEngine;
 using System.Collections;
 
 public class Movement : MonoBehaviour 
 {
     public float thrustMultiplier;
     public float rotationSpeed;
     private bool applyThrust = false;
     public Quaternion rotation = Quaternion.identity;
     public Rigidbody rb;
     
     void Start ()
     {
         rb = GetComponent<Rigidbody>();
     }
     
     // Check for misc keypresses
     void CheckMiscKeys ()
     {
         // Start applying thrust
         if (Input.GetButtonDown("Jump"))
         {
             applyThrust = true;
         }
         
         if (Input.GetButton("Fire3"))
         {
             applyThrust = false;
         }
     }
 
     // Check for rotation keypresses
     void CheckRotationKeys ()
     {
         float turn = Input.GetAxis("Vertical");
         if (Input.GetKeyDown(KeyCode.W))
         {
             rb.AddTorque(transform.forward * rotationSpeed * turn);
         }
         
         if (Input.GetKeyDown("s"))
         {
             rb.AddTorque(-transform.forward * rotationSpeed * turn);
         }
         
         if (Input.GetKeyDown("a"))
         {
             rb.AddTorque(-transform.right * rotationSpeed * turn);
         }
         
         if (Input.GetKeyDown("d"))
         {
             rb.AddTorque(transform.right * rotationSpeed * turn);
         }
     }
     // Apply thrust to the rocket's rigidbody
     void ApplyRocketThrust ()
     {
         if (applyThrust)
         {
             Vector3 force = transform.up * thrustMultiplier;
             GetComponent<Rigidbody>().AddForce(force);
         }
     }
 
     // Run physics calculations and misc events
     void FixedUpdate ()
     {
         CheckMiscKeys ();
         CheckRotationKeys ();
         ApplyRocketThrust ();
     }
 }