How: this is a relatively simple flow to manage, and it could be one part of a much larger bot if you prefer. All you'll need to do is set up the initial flow within Chatfuel to ask the user if they'd like to subscribe to receive content, and if so, how frequently they would like to be updated. Then you can store their answer as a variable that you use for automation.
A chatbot (also known as a spy, conversational bot, chatterbot, interactive agent, conversational interface, Conversational AI, talkbot or artificial spy entity) is a computer program or an artificial intelligence which conducts a conversation via auditory or textual methods. Such programs are often designed to convincingly simulate how a human would behave as a conversational partner, thereby passing the Turing test. Chatbots are typically used in dialog systems for various practical purposes including customer service or information acquisition. Some chatbots use sophisticated natural language processing systems, but many simpler ones scan for keywords within the input, then pull a reply with the most matching keywords, or the most similar wording pattern, from a database.