When a person starts a new conversation with your bot, you can set expectations with a get started flow to kickoff the experience.
To create your conversation trigger, simply navigate to your account's Triggers page and click "Create Trigger"
Then, click the 'Start a flow when a conversation is started by a contact' trigger:
You're ready to create your trigger:
Note that 'Channel' references the Page your Bot is attached to, while 'Flow' represents the flow you'd like to start when a contact initiates contact with your Bot.