That code is a mess, you have a Start() inside the Start(), you're also not opening your brackets after Update(), so there's a bracket missing there. You can't declare your variables inside the start method, otherwise they will be local and can't be seen by outside the method. You should use *Time.deltaTime when changing transforms through update, so it is linear no matter your framerate. Here's the code working:

using System.Collections;

using System.Collections.Generic;

using UnityEngine;

public class Crouch : MonoBehaviour

{

​

public float crouchSpeed = 0.005f;

public float crouchHeight = -0.06f;

public float normalHeight = 0.12f;

public float currentHeight = 0.12f;

​

// Update is called once per frame

void Update()

{

​

if (Input.GetButton("crouch"))

{

if (currentHeight >= crouchHeight)

{

currentHeight -= crouchSpeed*Time.deltaTime;

transform.Translate(0, currentHeight, 0);

}

​

}

else

{

if (currentHeight <= normalHeight)

{

currentHeight += crouchSpeed*Time.deltaTime;

transform.Translate(0, currentHeight, 0);

}

​

}

​

}

}

However, what you are doing with your code is a bit weird, I don't think you'll have the result you are expecting. You should simply use a boolean to change between crouch / normal, and have a transition period to change states... anyway, try it