After defining the source of the flow you must define a trigger, this defines when your flow starts:
Message received: Your flow will start when a new message is received, this is the most common trigger.
Call missed: You can't answer WhatsApp calls with 2Chat but enabling this trigger the flow will start when a call is missed.
Webhook Invoked: This is a trigger you can use to start a flow from an external app. After saving the flow you will get a public URL where an external application can send an HTTP POST request with variables that can be used in the flow to customize messages.
Flow triggers for automating WhatsApp group conversations:
Group Message Received: The flow will start when a new message is received on given group chat
Someone Joined a Group: This flow starts when a new participant joins a given group chat.
Someone Left a Group: Starts when a participant leaves a given group chat
Someone was removed from the Group: When a participant was removed by an administrator from given group chat you can use this trigger to create your automations.