A keyword is the first word in a message sent by the contact and can be used to start a flow. Once you have created a flow, you can create a new keyword trigger via the following steps:
Navigate to the "triggers" tab, then click the "Create Trigger" box.
Click the "Create a message keyword that launches a flow" option.
Enter your keyword, then select the flow you want it to trigger.
Optional: You can choose the group(s) to which your keyword trigger will apply. If you leave this field empty, your keyword trigger will apply to anyone who sends it.
Click "Create Trigger."
You can also create a trigger via assigning keywords to a flow while in the flow editor.
Up Next: Create a Message Keyword That Allows People to Join a Group