Are you talking about a formal documentation format or how to document in general?
The idea is that you should not focus on the "how". Just start documenting. Sharing your experience is a good start. You could write on a blogging platform (such as Medium) and just get your thoughts out there. If you don't want to make it visible to the public, then you could write a journal of some sorts. The important part is to start. Just start documenting and get as much as words as you can!
Here's the excellent blog post and video that gave me the inspiration to document every learning that I can.
These resources helped me start writing on Medium albeit my poor writing skills. I hope it can motivate you too!
TLDR: Just start 😀😁
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