How to use Input.GetAxis in if statement

Hey guys, i'm struggeling with Input.GetAxis right now. I would like to jump when pressing a button on my PS4 controller. I always get the error

error CS0019: Operator '&&' cannot be applied to operands of type 'float' and 'bool' GetAxis is not allowed to be called from a MonoBehaviour constructor (or instance field initializer), call it in Awake or Start instead. Called from MonoBehaviour 'PlayerController'.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerController : MonoBehaviour
 {
 
     public int speed = 5;
     public int turnSpeed = 100;
     public Rigidbody rb;
     public bool jumpingAllowance;
     public GameObject playerGun;
 
 
     // Start is called before the first frame update
     void Start()
     {
     }
     
 
     // Update is called once per frame
     void Update()
     {
         transform.Translate(Input.GetAxis("Horizontal") * speed * Vector3.right * Time.deltaTime);
         transform.Translate(Input.GetAxis("Vertical") * speed * Vector3.forward * Time.deltaTime);
 
         if (Input.GetKeyDown(KeyCode.R) && Input.GetKeyDown(KeyCode.W))
         {
             speed = 10;
         }
         else
         {
             speed = 5;
         }
 
         
     }
 
     void FixedUpdate()
     {
         if (Input.GetKeyDown(KeyCode.Space) && jumpingAllowance) 
         {
             jumpingAllowance = false;
             rb.AddForce(Vector3.up * 7, ForceMode.Impulse);
         }
 
         if(Input.GetAxis("Jump") && jumpingAllowance) 
         {
             jumpingAllowance = false;
             rb.AddForce(Vector3.up * 7, ForceMode.Impulse);
         } 
 
 
         
     }
 
 
     void OnCollisionEnter(Collision other)
     {
         if (other.gameObject.CompareTag("Ground"))
         {
             jumpingAllowance = true;
         }
         else
         {
             jumpingAllowance = false;
         }
 
     }
      
 }