Custom Field Settings: Lookup

Custom Field Settings: Lookup

I am trying to add a custom field to my notes to include contact details with the lookup feature, to be able to cross reference when doing a search in our notes. I am having problems with the related list label area. I dont know what to enter herer and zoho will not let me leave it blank. Could someone please let me know how to go about creating thei "lookup" contact field?
Thank you,
Mayra
Mayra