help me on how i can create lookup file in lookup editor

Greetings!! help me on how i can create lookup file in lookup editor I use to see a field called host that is identified by source IP and i want to add also another column that will describe that IP and its name is xyz name and i need to see by its name not only IP eg: if IP is 10.12.1.5 and the name ,how can you do it using lookup editor, kindly help me and guide me, I'm newest on splunk, Thank you!!