But if you use PagesController, you can add a ctp file super easily.
At first, create ctp file under \src\Template/Pages folder.
I created a test.ctp file under \src\Template/Pages.
Inside the file is:
<h1>Hello This is a test</h1>
Now you can access the file from browser without modifying controller or model. This is because Pages controller has a special function to display the ctp file.
The display function in PagesController. All you have to do is designate the file name.