This skill will be triggered every time your chatbot is idle (that means, there are no other skills being executed) and the user is sending a new message. The only exception is when you have LISTEN block in your conversation, and this block is currently active and is listening to the user’s input – in that case, the message will be saved to a specified attribute, and the “default” skill will not be triggered.
Chatbots use this skill to analyze what the user said and take action accordingly. This can be achieved in multiple ways, the most common approaches being keyword detection and natural language understanding.
For most scenarios, there will be no need to edit this skill manually, since its only function will be to forward the customer's message to the NLP engine to detect the underlying intent and launch one of your virtual assistant's skills.
/The standard "default" skill forwards customer's message to the NLP engine
Notice the use of the $_last_user_input system attribute (it contains the most recent message sent by the customer) to forward that message to the NLP engine.