Best starting point for the lore? Or even roadmap for beginners?

So I've heard some descriptions of the 40,000 lore from a podcast I watch, and it sounds incredible, but there's an awful lot of options to start from, with people recommending many different book series and youtube summaries. Is there a simpler approach, like just going into one standalone book to ground yourself before a bigger series? Or from a game to a tie-in book of some kind? Many thanks.