my calendar and contacts disappeared is there a way to get them back

If you mean you can't locate the Contacts and Calendar apps, swipe through all your screens. Those apps are pre installed and cannot be deleted.

Or use Spotlight > iOS: Understanding Spotlight Search

IF you're referring to your data (contacts and calendar events). Most likely you need to log into the email account you have them tied to again.

could be gmail, yahoo, outlook. Could be an exchange from work. Most likely you reset a password and now you just have to re enter it.