I have the following models, Item.php and Shipment.php set up. What I am trying to do is display the Item names, based on the shipment ID. I can access the shipments via $shipments = App\Shipment::where('id',4)->get(); but I am totally lost as to how to retrieve the item names, based on the Shipment model.

I am thinking something along the lines of $shipment->items()->getName or the like, but I cannot seem to wrap my head around it.

Item.php

<?php namespace App;

use Illuminate\Database\Eloquent\Model;

class Item extends Model
{

    protected $fillable = ['name',
        'description',
        'category',
        'condition'
    ];

    public function user()
    {
        return $this->belongsTo('App\User');
    }

    public function category() {
        return $this->hasOne('App\Category');
    }

    public function shipments(){
        return $this->belongsToMany('App\Shipment');
    }

Shipment.php

<?php namespace App;

use Illuminate\Database\Eloquent\Model;

class Shipment extends Model {


    protected $fillable = ['id',
        'item_id',
        'qty',
        'user_id'
    ];

    public function user(){
        return $this->belongsTo('App\User');
    }

    public function items(){
        return $this->hasMany('App\Item','id','item_id');
    }

It's important to know what a certain method will return. If it is a collection or a single model instance. This for example returns a collection (even if it only has one model in it)

App\Shipment::where('id',4)->get();

Instead use first() or just find() to add a where clause for the id and then only return one:

App\Shipment::find(4);

With the relationship it's similar. Since items is a hasMany relation, it will always return a collection. That means usually you will retrieve the items and loop over them:

foreach($shipment->items as $item){
    echo $item->name;
}

Also note that there's a difference between $shipment->items() and $shipment->items.
For more on that, read this answer.