Drush is a supporting tool, which is important for any Drupal developers. It helps executing a task with many steps simpler through one command. It's also really helpful in deployment process through integrating it in script.
I will share some basic Drush commands that I usually use:
1. Clear cache / Cache rebuild.
For Drupal 7
drush cc allFor Drupal 8/9
drush cr2. Delete all tables in the database (available on Drupal 7/8/9).