[otrs] Doubts in CustomerGroupSupport

Dear Sirs, I´m just giving the first steps in OTRS. When i was configuring user client group, the OTRS give me this message:

Sorry, feature not activ!

CustomerGroupSupport needs to be activ in Kernel/Config.pm, read more about this feature in the documentation. Take care!

I don´t understand why this feature is not active? Is there some kind of implications in a low level system? Best regards, Francisco Henriques