thinkphp-ThinkController:dispay method does not exist!

Recently, I wrote a program based on the teaching method in the ThinkPHP video tutorial and checked that there are no errors. The program has been shared on Baidu Netdisk, and the sharing address is: http://pan.baidu.com/s/1i5NSxZf. Please download and put it in the Apache root directory, enter http:localhost/thinkphp/admin.php?c=menu&a=index in the browser, and the following message will appear:
ThinkController: The dispay method does not exist (see the figure below for details)! May I ask why? what should I do?
There is a second question:
There are two sentences in the program: use ThinkController;
class IndexController extends Controller {
This means that there is a Controller folder under the Think folder, and there is a Controller class below it, but I am in the file The class file Controller.class.php file cannot be found in the ThinkPHPLibraryThinkController folder. Where is it?