To view your tasks from Todoist in a calendar, please go to the web-version of Todoist at todoist.com log in, click on the gear icon at the top and go to the Setting -> General. Here you can find an iCal feed at the bottom which you can add to any calendar software.
Please refer to this video to see how it works: https://www.youtube.com/watch?v=gzGubOy8GuE
As for email, there are two ways of managing emails with Todoist - by linking to them (which requires a plugin) or by sending/forwarding them (right-click on a project and choose "Email tasks to this project" for more info). Please check out this post on our blog where we compare both these options an their advantages: https://todoist.com/blog/2013/01/zero-inbox-policy-with-todoist/
Thanks. But how do I add it to ical?
Are you referring to the Calendar app on iOS? If so, please go to your phone's Settings -> Mail, Contacts, Calendars -> Add Account, select Other -> Add CalDAV Account or Add Subscribed Calendar and then paste the iCal feed from our site.