Sub Keywords allow you to setup custom responses for additional words following your keyword. They work in the format 'Keyword' 'Sub keyword' separated by a single space.
Setting up sub keywords is simple once you've already setup a keyword. Navigate to the Keywords & Textable Numbers section in the left navigation menu. Click the plus symbol to expand the sub Keywords list.
Add Sub Keyword to create a new Sub Keyword.
If you ever want to edit or delete a sub keyword all you have to do is click the plus symbol to reveal your list of sub keywords.