How to create a message
From Nexus Wiki
To demonstrate how to make a custom message for Fallout 3 or Fallout: New Vegas.
List of steps
1. Bring up the Geck and make sure that the correct master file is selected. This will either be Fallout3.esm or FalloutNV.esm.
2. Use the Object Window to open "Miscellaneous," and then open "Message." You should now see all of the vanilla messages.
3. Right-click above the vanilla challenges and select "New." This will open a dialogue box named "MESG."
4. Type in an ID with no spaces in the "ID" heading. This will identify your message when you want something to use it.
5. Type in the message you want displayed in the "Message Text."
6. Save your esp! You just made a message!
Messages such as these are often used to tell players that they completed a challenge or a mod has loaded something. For an example of how messages may be used, go to the how to create a challenge page.