Been dropped in the deep end. Where do I start?

I started work at a company who has several large Drupal sites 6 months ago. I told them straight up I didn’t have any experience in Drupal, but none-the-less I’m now creating modules and doing a lot of theming.

I’ve done a couple of courses online and have successfully set up Drupal sites at home and created themes and simple modules, but the complexity at work is way beyond any tutorials or courses I can find online. 6 months in and I’m still pretty stuck on every task I get (the stress factor is huge).

Where can I start learning about how Drupal modules and theming work at a more complex level?

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