Build a Rasa_chatbot only with Rasa_nlu

how to build a chatbot using Rasa NLU ?

Rasa NLU is the part of Rasa Open Source responsible for natural language understanding. It helps you to classify intents and extract entities. However, it misses the dialogue management part, which is crucial to build an assistant. So, you will not be able to predict the next action. If you want to build an assistant you need to use also Rasa Core.