Before you even write a single line of code, it's important to write a functional specification so the development team has a clear idea of what the bot is expected to do. The specification should include a reasonably comprehensive list of user inputs and expected bot responses in various knowledge domains. This living document will be an invaluable guide for developing and testing your bot.
In a traditional application, the user interface (UI) consists of a series of screens, and a single app or website can use one or more screens as needed to exchange information with the user. Most applications start with a main screen where users initially land, and that screen provides navigation that leads to other screens for various functions like starting a new order, browsing products, or looking for help.

“There is hope that consumers will be keen on experimenting with bots to make things happen for them. It used to be like that in the mobile app world 4+ years ago. When somebody told you back then… ‘I have built an app for X’… You most likely would give it a try. Now, nobody does this. It is probably too late to build an app company as an indie developer. But with bots… consumers’ attention spans are hopefully going to be wide open/receptive again!” — Niko Bonatsos, Managing Director at General Catalyst

[In] artificial intelligence ... machines are made to behave in wondrous ways, often sufficient to dazzle even the most experienced observer. But once a particular program is unmasked, once its inner workings are explained ... its magic crumbles away; it stands revealed as a mere collection of procedures ... The observer says to himself "I could have written that". With that thought he moves the program in question from the shelf marked "intelligent", to that reserved for curios ... The object of this paper is to cause just such a re-evaluation of the program about to be "explained". Few programs ever needed it more.
Some brands already seem to be getting the balance right. A bot needs to capture a user's attention quickly and display a healthy curiosity about their new acquaintance, but too much curiosity can easily push them into creepy territory and turn people off. They have to display more than a basic knowledge of human conversational patterns, but they can't claim to be an actual human -- again, let's keep things from getting too creepy here.
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.[1] 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.