Press F1 while VoiceAttack has focus to open VoiceAttackHelp.pdf in your default PDF viewer.
If you are unfamiliar with the more advanced features of VoiceAttack, the "Quick Input" action will likely be the simplest to use, as it does not require setting any variables beforehand.
Use the search feature of your PDF viewer to find these section: "'Quick Input'" , "Quick Input, Variable Keypress and Hotkey Key Indicators", "Text (and Text-To-Speech) Tokens" (which actually provides an example of using the "{RANDOM:}" token), and its subsection on the "{TXTRANDOM:value}" token.