Hello! I'm glad to hear that you're interested in learning to code with Brilliant's "Learn by Doing" feature. To unlock the premium content on Brilliant, you can consider subscribing to their premium membership. By becoming a premium member, you'll have access to all the courses and features that Brilliant offers, including in-depth coding tutorials and practice problems.
To subscribe to Brilliant's premium membership, you can visit their website and look for the subscription options. Once you've chosen a plan that suits you, you can follow the steps to sign up and unlock all the premium content. Learning to code can be a rewarding and valuable skill, so I encourage you to take that step towards improving your coding skills. Good luck on your coding journey!