Skills vs Certification Tracks

Content

Can someone please explain the difference between the two? 

I'm starting to bring in content that will be accessible as part of a self-enroll option. I'd like to be able to flag completion of these activities in two ways. I want to provide the end user with recognizition of their work and also begin to develop a tracking workflow to monitor users associated with the specific task.

Something like ...

End user: You've completed the Microsoft Basic elearning and have earned the "Excel Beginnger" skill.

Organization: I can run a report to display a list of users who have this skill or completed an Excel Basic certification track. The latter might be paired with an ILT session to make the track more meaningful.