What are the models for Laravel 5.3 for?

Excuse my ignorance. I create the models in the following way:

php artisan make:model Marcas -m

And the model I leave it as it is created:

namespace App;

use Illuminate\Database\Eloquent\Model;

class Marcas extends Model
{
    //
}

I modify the migrations like this:

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateMarcasTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('marcas', function (Blueprint $table) {
            $table->increments('id');
            $table->string('nombre');
            $table->string('descripcion');
            $table->boolean('status');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('marcas');
    }
}

I manipulate all the functions from the controller that created it like this:

php artisan make:controller MarcasController --resource

And I modify it until it looks like this:

namespace App\Http\Controllers;

use Illuminate\Http\Request;

use App\Http\Requests;

use Illuminate\Contracts\Auth\Guard;
use Closure;
use Auth;
use Session;
use Redirect;
use DB;
use PDO;
use Validator;
use Response;
use Datatables;
use Debugbar;
use Alert;
use Illuminate\Support\Facades\Input;
use App\Marcas;

class MarcasController extends Controller
{
    protected $auth;
    public function __construct(Guard $auth){
        $this->auth = $auth;
        $this->middleware('auth');
        $this->middleware('ruta:Marcas');
        $this->middleware('funciones:Marcas,crear',['only'=>['crear']]);
        $this->middleware('funciones:Marcas,editar',['only'=>['editar']]);
        $this->middleware('funciones:Marcas,eliminar',['only'=>['eliminar']]);
        $this->middleware('funciones:Marcas,estado',['only'=>['estado']]);
    }
    /**
     * Display a listing of the resource.
     *
     * @return \Illuminate\Http\Response
     */
    public function index(){
        return view('marcas.index');
    }

    public function tabla(Request $request){
        try{
            $sql = Marcas::select(array('id', 'nombre', 'descripcion', 'status'));
            return Datatables::of($sql)
            ->addColumn('action', ' Editar  Eliminar')
            ->addColumn('estado', 'activo')
            ->filter(function ($query) use ($request) {
                if ($request->has('campo')) {
                    $query->where(DB::raw("CONCAT( nombre, ' ', descripcion )"), 'ilike', "%{$request->get('campo')}%");
                }
                if ($request->has('status')) {
                    $query->where('status', '=', "{$request->get('status')}");
                }
            })
            ->make();
        }catch(\Illuminate\Database\QueryException $e){
            $array = array(
                'mensaje' => $e->getMessage(),
                'codigo' => $e->getCode(),
                'sql' => $e->getSql(),
                'bindings' => $e->getBindings(),
            );
            return Response::json(array('ErrorSql' => $array));
        }
    }

    public function crear(Request $req) {
        $rules = array(
            'nombre' =>  'required|unique:cargos|min:5|max:30',
        );
        $validator = Validator::make ( Input::all (), $rules );
        if ($validator->fails()){
            return Response::json(array('errors' => $validator->getMessageBag()->toArray()));
        }else{
            try{
                $cargos = new Marcas();
                $cargos->nombre = $req->nombre;
                $cargos->status = 't';
                $cargos->save();
                return Response::json(array('correcto' => $cargos->toArray()));
            }catch(\Illuminate\Database\QueryException $e){
                $array = array(
                    'mensaje' => $e->getMessage(),
                    'codigo' => $e->getCode(),
                    'sql' => $e->getSql(),
                    'bindings' => $e->getBindings(),
                );
                return Response::json(array('ErrorSql' => $array));
            }
        }
    }

    public function editar(Request $req){
        $rules = array(
            'nombre' =>  'required|min:5|max:30',
        );
        $validator = Validator::make ( Input::all (), $rules );
        if ($validator->fails()){
            return Response::json(array('errors' => $validator->getMessageBag()->toArray()));
        }else{
            try{
                if(Marcas::where('nombre', 'ilike', $req->nombre)->where('id', '', $req->id)->exists()){
                    return Response::json(array('encontrado' => 'nombre ya ha sido registrado'));
                }else{
                    $cargos = Marcas::find ($req->id);
                    $cargos->nombre = $req->nombre;
                    $cargos->save();
                    return Response::json(array('correcto' => $cargos->toArray()));
                }
            }catch(\Illuminate\Database\QueryException $e){
                $array = array(
                    'mensaje' => $e->getMessage(),
                    'sql' => $e->getSql(),
                    'bindings' => $e->getBindings(),
                );
                return Response::json(array('ErrorSql' => $array));
            }
        }
    }

    public function eliminar(Request $req){
        try{
            Marcas::find($req->id)->delete();
                $array = array(
                    'mensaje' => 'todo bn',
                );
                return Response::json(array('correcto' => $array));
        }catch(\Illuminate\Database\QueryException $e){
            if($e->getCode()==23503){
                $array = array(
                    'mensaje' => $e->getMessage(),
                    'sql' => $e->getSql(),
                    'bindings' => $e->getBindings(),
                );
                return Response::json(array('ClaveForanea' => $array));
            }else{
                $array = array(
                    'mensaje' => $e->getMessage(),
                    'sql' => $e->getSql(),
                    'bindings' => $e->getBindings(),
                );
                return Response::json(array('ErrorSql' => $array));
            }
        }
    }

As I read in this article: link It says that there we define which fields we can modify, eliminate, etc. But I do not play them in the Laravel models and everything is fine.

What really do the models in laravel.