How can l use DotnetNuke to create a website like this http://www.doctorspring.com/ IS a site where people can chart with a doctor
That is a very generic question, but I would start by finding a chat (I suppose you mean chat not chaRt).
Here are a few:
https://dnnchat.codeplex.com/
http://store.dnnsoftware.com/home/pro...
Cheers,
Aderson