Error CS0019 in unity 3d code, how to fix?

Question

C++ / C#

I just started learning unity with C#, I decided to make a simple puzzle game, I wrote the code to make the object move along the x, y axes. Gives an error message

Assets\Player.cs(15,4): error CS0019: Operator '+=' cannot be applied to operands of type 'Vector3' and 'int'

. Help me fix it, I've already broken my head.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Player : MonoBehaviour
{
  //int KeyOne;
  //int KeyTwo;
  int moveDirection;
  private void FixedUpdate()
    {
    //if(Input.GetKey(KeyOne))
    if(Input.GetKey(KeyCode.W))
    {
      GetComponent<Rigidbody>().velocity += moveDirection;
    }
    //if(Input.GetKey(KeyTwo))
    if(Input.GetKey(KeyCode.S))
    {
      GetComponent<Rigidbody>().velocity -= moveDirection;
    }
  }
}

Answer 1

Are you able to read? How to add a number to a vector?
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