The neat thing with Emacs is that the core concepts of the system are all first-class programming entities with their own documentation. So if you want to know what your current mode does, you can use C-h m to get a bunch of information including commands, key-bindings and links to code. If you have a key command, you can use C-h k, enter the keys, and you'll see exactly what function that command runs. You can get info about functions with C-h f and variables with C-h v; coupled with some kind of fuzzy-find-autocomplete (which, unfortunately, isn't set up by default), it's usually pretty quick to find the functions and config options that are relevant to whatever you're trying to do.

I still use web searches to look up Emacs things occasionally, but the built-in help commands are still useful because they're naturally tied to (and organized by) the core code entities that power Emacs.