Like we used to do math in our school days, if we had some questions that we are not able to solve, then we used to see the math book and solve the question.

In the same way if a developer wants to make something that he/she has never made before, then from where they see, learn and make it ?

For example – If someone has to make the TikTok and Instagram both frontend and backend then from where they can take reference, study and can make it ?

If someone wants to make the backend of TikTok, Uber or any other platform or want to create something new backend. From where they can reference, study and create it ?

I have tried to find answer to this question but did find any good answer. Please answer this.