Most gamblers know very well how to play certain games and don't really need any tutorials. How often does someone go to a physical casino, take out a $100 bill and go to a Blackjack table and just guess how to play the game? Almost never. They probably won't even want to risk betting $1 if they didn't know what they were doing. Hence this is the reason why many of the traffic to casinos usually just plays slots since its pretty much automatic as soon as you pull the lever. Either money comes out meaning you've won or nothing happens which means you lost.
You are partially right. A major portion of gamblers do know what they are doing thanks to their experience, but the posters above are discussing sports betting which could get complicated for newbies looking to bet for the first time in their life.
Terms like Handicap, Accumulator etc would confuse them which is why guides are essential(DarkoReborn already shared the links though).
Yes, if they think there is any sort of person that just goes to casinos knowing everything about gambling all the time and no rookie ever sets foot in a casino then they are direly wrong.
I have worked in casinos before and I have met with a lot of people who had no idea how to gamble but just wanted to feel the thrill of gambling so they were there playing without exactly knowing how it all works. Not even complicated games neither, I literally mean the most common games like slots and some people had no idea how it all worked.
So all in all, the question is not "is there people who have no idea how gambling works but gamble anyway", question should be "Should the casino feel responsible for those people?"