Adding Lead and/or Contact Records to a Campaign is dependent on first creating a filter. If do not know how to create a filter, or need a refresher, please review the video on Creating Filters. Once your filter is created, navigate to your campaign record and scroll down to the module that contains the filter (Leads or Contacts). Choose the filter from the dropdown, and select 'Load List'.

Users also have the option to add records outside of a filter by choosing the 'Select' button, or create a record on the fly to relate to the campaign by selecting the 'Add' button.