GoIP.de is a dns provider for easy to use dynamic DNS. You will get a static address (subdomain below goip.de), which you can use with the dynamically changing ip address of your home network. Often your internet provider will assign you a changing ip (dynamic ip address) only. This makes it complicated to access home services from the internet. With GoIP.de your network will be accessable from a static hostname.
GoIP.de allows an easy and fast access to services running on your private computer or network like web, ftp, game or voice servers. You do not have to find out, what your current ip address is as you can always just use your GoIP.de subdomain. Friends and other persons can also use your services without asking for your ip address.