You can't, basically. All the certifications are scams. The best is the CSCS but even that is watered down. Buy Starting Strength by Mark Rippetoe and read it

You can't, basically. All the certifications are scams. The best is the CSCS but even that is watered down. Buy Starting Strength by Mark Rippetoe and read it front to back. Then watch his videos/DVDs. Then execute the movements per the book and video them.