How to populate contacts list for campaign under the contacts tab?

You can create your target list for campaign directly from the contact page:

Select contact(s) that you want to reach out to, click on the Campaign button

Steps:
  1. You can create a campaign list or add to the existing list
  2. Give the campaign list name
  3. Click on Create List
  4. Click on ok.
A campaign list will be successfully created Or you can choose an existing list to add the selected contacts to