Example: example.cpp
The cpp in the above example would be the file extension.
Under the Windows OS this can be seen or made unseen by opening a file folder, selecting Tools from the menu bar and selecting the Folder Options.... This will display the Folder Options dialog.
From this dialog select the View tab. Having a check in the Hide file extensions for known files type setting will enable you to see the file extensions.
I am not sure what you do under a Linux file manager. At the command line the file extension are shown automatically. This is also true for a Windows console command line also.
