Once you've run the build commands at the end of the page, navigate to your project folder. You should see a build folder and an src folder. src is generally where your source and/or header files. build is where the makefile sits. Navigate to build folder and open it in terminal. Then, nagivate to bin folder inside the build folder. This is where the executable sits; double clicking it should run it and cause the window to open. To rebuild the project, run the same commands from the end of the tutorial again in the terminal, from the project's folder (none of its subfolders).

Once you've added more files to your project, you might have to change the CMakelists.txt in your project folder to account for it.

That's pretty much it. It took me forever to figure that out.