It doesn't require a packet radio link, telnet, or any complicated software or setup, only an internet connection is required.
A DX Cluster is a way for DXers to share tips on what stations they are currently hearing. Stale DX news is useless, so a DX Cluster allows people to share their loggings within seconds.
Just download the program, enter in your Name and location, and that's it. Loggings from other listeners will be displayed on the cluster screen in real-time.
You can submit your own loggings as well of course. You can also filter the types of loggings you want to see, so you don't have to see stations that you have no interest in.Clicking on a logging line will bring up a window with some more detailed logging information, and eliminates the need to horizontally scroll to see the comments/etc on the right side.