You are missing lots of information that could help others help you.
What is the make/model of the printer?
Is it directly connected to the network or connected to another computer on the network? If the latter, what is the OS on that other computer? If the former, can you ping the computer?
When you refer to the "Add Printer" button, is that in some system settings dialog; if so, what desktop environment are you using?
Have you tried to add the printer via CUPS (
http://localhost:631)?