Here's a quick video of the process :)
Creating a Keyword:
1. Choose 'Keywords' from the Messaging menu on the left
2. Click the green 'Create New Keyword' button
3. Enter the keyword details: Keyword, Topic, and Form Fields
4. Click the checkbox next to the list(s) you'd like the person to be added to
6. Add a message
Note: The message will display after the form has been submitted
7. Click the green 'Save changes' button to create a keyword
Plus: You can view an SMS preview, as well as the Form Preview
Archiving a Keyword:
1. Choose 'Keywords' from the Messaging menu on the left
2. Find the keyword you would like to archive
3. Click the button with the 3 dots to show more options
4. Click 'Archive Keyword' to archive the form