Kerberos V5 is a single-sign-on system. This means that you only have to type your password once, and the Kerberos V5 programs do the authenticating (and optionally encrypting) for you. The way this works is that Kerberos has been built into each of a suite of network programs. For example, when you use a Kerberos V5 program to connect to a remote host, the program, the KDC, and the remote host perform a set of rapid negotiations. When these negotiations are completed, your program has proven your identity on your behalf to the remote host, and the remote host has granted you access, all in the space of a few seconds.
The Kerberos V5 applications are versions of existing UNIX network programs with the Kerberos features added.