First you need to create the Registration Group:

  1.  > onMessage > Approval > Event Registration
  2.  Search for Event Registration
  3.  Click Edit for Event Registration Form
  4.  From left hand menu, select Registration Items
  5.  Click Add Group
  6.  Mark if the Group is Required, give it a title and who can attend (Public or Private)
  7.  Click Save & Exit

Then you need to create the actual Registration Item:

  1.  Click Add Item
  2.  Mark the item as required, give it a start and end date, and select the Fee Type(per attendee, per item, etc) and set the amount
  3.  Select Save & Exit