How to remotely access a server

You would need to forward the ports for the server within the time capsule settings.
Don't have a time capsule, so I don't know how accurate this is still:
http://must-know-mac.blogspot.com/2008/07/how-to-port-forward-time-capsule.html

and connect using your external IP (provided by the ISP, may change frequently depending on the provider). The easiest way to find it is with a website, ie: showmemyip.org or ipchicken.com

 

192.168 addresses are indeed local and of no use to you. You need the external IP address, which you can get with many websites. Just search for it. As for screen sharing, that would take knowledge of port forwarding, on the airport extreme/Time Capsule this is called port mapping. You have to direct the ports externally to the proper IP address on the network.

Here's a step by step of how to do it:

1. Open Airport Utility on the Mini. Your Time Capsule should be automatically selected.
2. Click the "Manual Setup" button.
3. Click the "Advanced" tab.
4. Click the "Port Mapping" sub-tab.
5. Click the "+" to create a new port mapping
6. From the "Service" list, select "Apple Remote Desktop"
7. Change the IP address, to the one reported by the Mini.
8. Click "Continue", then "Done", and then "Update".

That's how you do it for Screen Sharing. Address Book/iCal server sharing can be done too, but not via the drop down "Service" menu. You have to specify the ports manually instead of selecting an option in that menu. To access this, use the external IP reported by websites or under the "TCP/IP" sub-tab under the "Internet" tab.

 

Be aware also that by using their public IP and port forwarding the request for screen sharing to your friend's Mac, you're opening up Screen Sharing to anyone on the internet who stumbles across their IP.

Better use a strong password.

 

Can also install TeamViewer personal and create a free account to access it

Apple Desktop is better but with TeamViewer don't need to open ports and all