There are two main reasons why contacts have populated in the 'skipped' column in your campaign stats:
The nature of campaigns is that they are forward looking only — contacts who met the criteria of the campaign in the past will be 'skipped' upon setting the automation live.
If you've paused your automation, contacts who met the entry condition(s) whilst the automation was not live will not enter the campaign once it's restarted, but will instead be skipped.
If you would like to enroll one of the 'skipped' contacts into the automation, you can add their email address via the 'Add Contacts' button on the automation.
Remember to ensure the campaign and campaign messages are live before adding a contact in this fashion!