Many to Many saving data

I have the following schema

Schema::create('users', function (Blueprint $table) {
    $table->increments('id');
    $table->string('userName')->default('');
    $table->string('userEmail')->default('');
    $table->tinyInteger('active')->default(1);
    $table->timestamps();
});

Schema::create('user_groups', function(Blueprint $table)
{
    $table->increments('id');
    $table->string('groupName')->default('');
    $table->timestamps();
});

Schema::create('users_user_groups', function(Blueprint $table)
{
    $table->integer('userId')->unsigned()->index();
    $table->foreign('userId')->references('id')->on('users')->onDelete('cascade');
    $table->integer('userGroupsId')->unsigned()->index();
    $table->foreign('userGroupsId')->references('id')->on('user_groups')->onDelete('cascade');
    $table->timestamps();
});

Essentially, a User can be apart of many Groups, and a Group can have many Users.

class User extends Model
{
    protected $table = 'users';
    protected $guarded = [];

    public function groups()
    {
        return $this->belongsToMany('App\Group', 'users_user_groups');
    }
}

class Group extends Model
{
    protected $table = 'user_groups';
    protected $guarded = [];

    public function profusionUser()
    {
        return $this->belongsToMany('App\User', 'users_user_groups', 'userId');
    }
}

I think the Models are ok. I then have an updateUsers function in my controller

public function updateUsers()
{
    $users = Helper::returnUsersFromLdap();

    DB::table('users')->update(array('active' => false));
    foreach($users as $userName => $userData) {
        $user = User::firstOrNew(['userName' => $userName]);

        foreach ($userData as $userEmail => $userDepartment) {

            $user->userEmail = $userEmail;
            $user->active = true;

            $userGroups = Helper::returnGroupsFromLdap($userEmail);

            foreach($userGroups as $group) {

            }
        }
        $user->save();
    }

    Session::flash('flash_message', 'Users updated');
    Session::flash('flash_type', 'alert-success');
    return Redirect::route('users.index');
}

I essentially get a user list from Active directory, loop this, and add the my users table. For each user, I call returnGroupsFromLdap passing the users email as a parameter. For each user, this will return the groups that user is in like so

array:3 [▼
  0 => "Group1"
  1 => "Group2"
  2 => "Group3"
]

My question is how can I link the user groups to a user? So I loop each group and then add it to my user_groups table? But then where do I populate the pivot table I created?

Any advice on this matter appreciated.

Thanks

via Chebli Mohamed