Agent code feature is a third party dealing interface between customer and hotel management. It can be setup under Features>>Travelling Agent. Commission will be given to agent based on commission types under Features>>Travelling Agent.
Referral is just information about the hotel from any secondary source like friends, newspapers, magazine…etc. For Referrals, commissions are not applicable to any secondary sources. It can be setup in Setup>> Advanced Easy InnKeeping>> Referral Types.