Laravel:Undefined property: Illuminate\Database\Eloquent\Collection::$id

i want the current user when add user in a team will save in database user id for this user not id for current user but when i use $user=User::all(); or $user=User::find($id); don't work and have error Undefined property: Illuminate\Database\Eloquent\Collection::$id and when use $user=Auth::user(); save the current user id

public function addUser($id) {

        $teams =TeamWork::find($id);

        $user =User::all();

        $teammember = new TeamMember;
        $teammember->user()->associate($user->id);
        $teammember->Teamwork()->associate($teams->id);
        $teammember->save();

        $users = User::pluck('username');

    return View('teams.adduser' , compact('users'))->with('teams', $teams);


  }