Q: How do I access my time capsule from another city?

The simplest way....which is also probably the best way......for users to connect to the AirPort Time Capsule from a remote location is set up Apple's Back To My Mac (BTMM) option on your Mac and AirPort Time Capsule.  Apple's instructions for this are here:

Set up and use Back to My Mac - Apple Support

Apple does not offer software to allow the iPad to connect back to the Time Capsule, so if you are interested in doing that, you will need a 3rd party solution for the iPad......FileBrowser is a popular choice.  But, this is not easy, and will require that you set up your main router for what is known as Port Mapping and use some some advanced configuration settings in the FileBrowser App. 

FileBrowser support can offer some tips on that topic, which is beyond the scope of what we can offer on this forum.

Stratospherix - FileBrowser - Overview

http://www.stratospherix.com/support/gsw_timecapsule.php?page=6remote