Once you find a particular computer, there are all sorts of ways to find the data on it. Directories are just special-purpose servers on the Internet Most commonly, the directories we use to find a particular computer are themselves hosted on other computers on the Internet. IP addresses that are easier to find, or are more stable, than what we are looking up. There is nothing magic about any specific system. You find a person or business' current phone number or address through directories like the Yellow Pages, or your own address book.
Nothing is permanent.
People move and their number and address changes. Area codes and even Zip codes are changed without changing the physical address. Sometimes it isn't unique , like a name in a phone book, and you need to use other information to choose which entry is appropriate. Different directories are set up for different purposes, and often there are multiple directories you can use to find the address you want. You often choose the directory to use based on what information you have as a key to search the directory and other properties of the directory.