To become an Emacs expert, learn where to find information about Emacs.
Over the fifteen years I've been using Emacs, I've learned a whole lot about it. My packages have over 50,000 downloads, and I've presented at EmacsConf 2020. I co-organize EmacsNYC. In that time, I've found the best place to ask questions about Emacs...is Emacs!
Here's how you can ask Emacs questions.
1. The Emacs tutorial -- C-h t
Emacs's built-in tutorial is incredibly well-written. It takes you from knowing nothing all the way through undo and redo, autosaving, and window management.
2. Show functions and variables -- C-h f, v
Press C-h f and type the name of a function to view the documentation for that function. C-h v views a variable's documentation. If Emacs's source is installed, you can click on a hyperlink to go the function's source.
Emacs's documentation is comprehensive. It explains what a function does, and what its arguments are, but the documentation viewer even also tells you what keypresses that function is bound to! This works not only for built-in key bindings, but any you have added.
3. Show what function is bound to a particular keypress -- C-h k
To ask Emacs what will happen when a certain key or series of keys is pressed, type C-h k, then the key you are interested in. This brings up the same documentation from C-h f, with the same detailed information.
4. Show what keys are bound in the current buffer -- C-h b
If you don't know what you can do in the current buffer, ask Emacs! C-h b lists all the functions currently bound.
If you have a multi-key binding, you might not know what comes next. After beginning any prefix, press C-h to show bound keys after that prefix. Even an Emacs pro will learn something new with C-x C-h.
5. View documentation about active major and minor modes -- C-h m
To see documentation for the modes that are currently active, ask Emacs! C-h m displays the mode descriptions plus bound keys.