Google is your best friend

If you have a problems or questions related to Drupal it is usually very easy to find the required help online. Copy and paste the exact error message, and consider putting the search term inside double quotes so that Google does a literal search. Alternatively you can ask a question like "Drupal how to create a subtheme".

Google example search for Drupal "How to create a sub theme in Drupal"
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Drupal themes to be compared