There are many free program editors available on the Internet. You can download one of these tools and use it to write your source programs.
One of the best totally free editors that works in Windows is called Notepad++. You should use Google to find out from where you can download Notepadd++. After you have downloaded the setup or installer file, you should just run it.
Other free editors include Sublime Text and Microsoft Visual Studio Code. These work both in Windows and in macOS.
If you decide to use Notepad++ and work with the programs presented on this site, you should set the indentation step to 3 and use spaces in indentation of program lines. To make these, you should select Settings -> Preferences -> Language, and set Tab size to 3 and select Replace by space.
If you decide to use some other editor, or an IDE (Integrated Development Environment), you should make the above settings if you decide to modify the programs presented on this site.