where is the window to type "run composer install" ?

apologies for posting a dummy’s question, but I am not a developer but small business owner.  I have successfully built drupal 7 sites entirely with the drupal web interface and e.g. filezilla, and am just trying to get to grips with Drupal commerce in Drupal 8. I keep seeing references to composer starting with for example “run composer install” with in the commerceguys kickstart package – but where do I find the place to actually type that? 

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