Request review for correct methodology (new to lavarel)

New to lavarel, managed to get something done but unsure if I did this the correct way. -> Can somebody please review my code so I can learn how to do this properly?

Goal: I would like to add users to administrations, for this I have created the following:

The model: (after alot of reading I get in to alot of trouble if I added functions to the model, so I left this blank, i'm unsure of how to add my functions here and call them properly from the controller, if anybody has a live example, I would be happy to give it another bash)

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use App\administration;

class Administrations_has_users extends Model
{
    protected $table = 'core_administrations_has_users';
}
?>

migration database tables:

<?php
Schema::create('core_administrations', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('user_create')->nullable();
            $table->integer('user_update')->nullable();
            $table->string('name')->unique();
            $table->text('description')->nullable();
            $table->binary('image')->nullable() ; // for blob
            $table->integer('type')->nullable();
            /*
            Types:
            1 = ?
            2 = ?
            3 = ?
            */
            $table->timestamps();
        });
Schema::create('core_administrations_has_users', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('userId');
            $table->integer('administrationId');
            $table->integer('type');
            /*
            Types:
            1 = member
            2 = owner
            */
            $table->timestamps();
        });
?>

• users table is default of the lavarel

administrationController:

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use App\Administration;
use App\Administrations_has_users;
use Auth;
use Session;
use App\User;
use App\Sysevent;
use DB;

//sf administrations group users together and are also commonly used by apps. These will mostly represent companies.

class AdministrationController extends Controller
{
    public function index()
    {
        $posts = Administration::orderBy('id', 'desc')->paginate(10);
        
        //need users and administration list for the add to administration form
        $users = User::all();
        $administrations = Administration::all();
        
        return view('administrations.index')->withPosts($posts)->withUsers($users)->withAdministrations($administrations);
    }

    //HIDDEN OTHER FUNCTIONS THAT I WILL NOT BE NEEDING FOR THIS
    
    public function assign(Request $request)
    {
        //get params
        $user = $request->userId;
        $administration = $request->administrationId;
        $type = $request->administrationType;
        
        //check if user exists
        $checkUser = user::where('id', '=', $user)->first();
        if ($checkUser === null) {
            Session::flash('success', 'User does not exist');
            return redirect()->route('administration.index');
        }
        
        //check if administration exists
        $checkAdministration = Administration::where('id', '=', $administration)->first();
        if ($checkAdministration === null) {
            Session::flash('success', 'Administration does not exist');
            return redirect()->route('administration.index');
        }
        
        //check if user is already part of the administration
        if ($checkAdministration = DB::table('core_administrations_has_users')->where([
            ['administrationId', '=', $administration],
            ['userID', '=', $user],
            ])->exists()) 
        {
            Session::flash('success', 'User is already part of that administration');
            return redirect()->route('administration.index');
        }
        
        //are you trying to make an owner type? if so, you need to make sure there isn't one already
        if ($type == '2' && $checkOwnerExists = DB::table('core_administrations_has_users')->where([
            ['administrationId', '=', $administration],
            ['type', '=', '2'],
        ])->count() > 0)
        {   
            Session::flash('success', 'An owner has already been assigned');
            return redirect()->route('administration.index');
        }
        
        //if all of the above past then add the user to the administration
        $input = new Administrations_has_users;
        
        $input->userId = $user;
        $input->administrationId = $administration;
        $input->type = $type;   
        $input->save();
        
        //create System event
        $sysevent = new Sysevent;
        $sysevent->event = 'User assigned to administration';
        $sysevent->type = 2;
        $sysevent->save();
        
        //set flash data with success message
        Session::flash('success', 'User assigned to administration');
        
        return redirect()->route('administration.index');
    }
}
?>

administration index view:

<?php
        <div class="row">
        <div class="col-md-12">
            <div class="card-box widget-box-1 bg-white">
                <h4>Add user to administration</h4>
                <form method="POST" action="{{ route('administration.assign') }}" accept-charset="UTF-8">
                    
                    {{ csrf_field() }}
                    
                    <label for="name">Select user: </label>
                    <select name="userId" class="selectpicker">
                        <option value="" selected="selected">Please select a user</option>
                        @foreach ($users as $user)
                        <option value="{{ $user->id }}">{{ $user->name }} - {{ $user->email }}</option>
                        @endforeach
                    </select>
                    <br>
                    
                    <label for="name">Select administration: </label>
                    <select name="administrationId" class="selectpicker">
                        <option value="" selected="selected">Please select an administration</option>
                        @foreach ($administrations as $administration)
                        <option value="{{ $administration->id }}">{{ $administration->name }}</option>
                        @endforeach
                    </select>
                    <br>
                    
                    <label for="name">As: </label>
                    <select name="administrationType" class="selectpicker">
                        <option value="1" selected="selected">a member</option>
                        <option value="2" selected="selected">the owner</option>
                    </select>
                    <br>
                    
                    <button type="submit" class="btn btn-sm">Execute</button>
                    
                </form>
            </div>
        </div>
    </div>
?>