I am creating a chatbot for my website, I want to add clickable images, links, buttons in chatbot using Web demo in APIAI. How Can I achieve this?
You can't achieve it using Web demo. As name says it is only demo where you may test flow of your dialog - if api really can transform your language into intent ;) So good to share with your friends and ask them for feedback and maybe improve your feed data - not for a rich client in production.
You may build you own client using their javascript sdk for example - https://github.com/dialogflow/dialogflow-javascript-client. If you know html, css and basis of javascript you should be good to go.