Are you looking to export the Intervals calendar in iCal format? If so the home page can be exported in iCal format and then imported into another program. Here is a blog post on the functionality. If you are hoping to import an iCal file into Intervals this functionality does not currently exist but tasks, milestones and projects can be imported in CSV format by navigating to Options >> Settings & Defaults >> Import Data.
If you do not see the link to Settings & Defaults your best best is to click on the find a bug link from within your account to notify our support team direct. They can check your user level and account to see if you have access to the link. If you are an administrator level user on your account that has access to both plan info and settings and defaults here is what the menu should look like: