Enabling an Alexa skill is a simple process which adds the skill's abilities to your Alexa's lexicon.
and select Skills & Games, then search for "PC Commander" and select the skill from the list.
Once you're done enabling the skill, if you wish to use Push2Run as your listener program to kick off actions on your computer, see this guide on how to integrate with Push2Run.
Next, read the wiki on how to use the skill.
Or just start using the skill by saying "Alexa, open my computer" and follow its lead.