Several topics in this help file mention creating and/or editing text files to configure or otherwise direct GPSS functions or features. You use a text editor to do this. If you already knew this, read some other topic or, better, take your computer and GPSS on the road. Any road. It will be harder for you to get lost.
This topic exists because many otherwise normal people have no knowledge of text editors. Text editors are used by those who write language-based computer code, such as C, ADA, and QuickBasic. Windows (and previously, DOS) has included a free one called Notepad for many years. Text editors are less employed these days, since there are many visual development environments such as Visual Basic.
Text editors are basic word processors that save files as text (ASCII) code. You can use a full-featured word processor such as Microsoft Word, then save the file as a text file, but Word offers 5 text file types, and there is some controversy as to which type you want. (The type you want is plain MS-DOS text... we think). Notepad keeps it simple by not giving you any choices and whatever the file structure is, it works with most language-based programs.
You find Notepad under Programs > Accessories. Once you fire it up, don't worry about type font, margin spacing, italic/bold or any of the more nifty formatting things in full word processors. You don't need any of this. Just use the settings you find when you fire it up.
Free replacement text editor
If you tire of the plain Jane and featureless Notepad, you might consider a free replacement. There are several. Our favorite is ConText.