How to get data from related table in Laravel (one to many)?

In Order model you need to use the belongsTo relationship:

public function user()
{
    return $this->belongsTo("App\User"); // second and third arguments are unnecessary.
}

In User model you can use hasMany relationship, for example in:

App/User.php

Add

public function orders()
{
   return $this->hasMany("App\Order", "user_id", "id");
}

Now you can use this:

return User::find(1)->orders;

If you want to retrieve the all the Orders belonging to the current user, try using following function.

public function index()
{
    $orders = Auth::user()->with('Orders')->get()->toArray();//To get the output in array
    /*        ^               ^
     This will get the user | This will get all the Orders related to the user*/

    return response()->json($orders);
}

As pointed out by @Martin Heralecký, you would also need to change the hasOne() to belongsTo() in Order Model. See following (copied from @Martin Heralecký answer)

public function user(){
    return $this->belongsTo("App\User");// second and third arguments are unnecessary.
}

Why belongsTo():

has_one and belongs_to generally are same in a sense that they point to the other related model. belongs_to make sure that this model has the foreign_key defined. has_one makes sure that the other model has_foreign key defined.

Your $orders array will look something like this:

User => [
 id => 'user id',
 name => 'user name'
 orders => [
  0 => [
         //order data
       ]
  1 => [
         //order data
       ]
       .
       .
       .
       .
   ]
]