the main documentation page of /e/ helps and the howto category in this forum → enter a search term inside the howto category and it will offer to scope the search to the category you’re currently in (howtos) - I found this very useful.
There’s a list for all system apps at List of HOWTOs & add your suggestions
For switching lens in camera, that instruction is linked to the Camera Apps project docs where it explains to use the “Switch multi-camera icon” or “Switch Camera” to cycle through the lenses