Purchasers and Operators are setup in Sub-Account Maintenance, which carries information across all modules.
Purchasers are usually setup in the Check Stub system but can also be setup in the Production system.
Operators are related to the First Purchaser system. The Purchaser tab is First Purchaser Only.
NOTE: To add or remove tabs, go to General Ledger > Master File Maintenance > Sub-Table Maintenance, find the Sub-Table you are working in (either Operators or Purchasers), check/uncheck each box you would like to see/not see.