They don't tell them anything. There's just no education whatsoever in the system for how to date, how to deal with a wife, with kids, etc, etc.
So everything is just secondhand misinfo.
A marriage does not come with a user's manual. And you can't Google the instructions either.
Every marriage is a world of its own, and what works for one marriage might not work for another.
Now, there are some general facts that are handy to know in advance, but to an unmarried individual, these facts go into one ear and out the other. (Imagine reading a setup manual for a treadmill when you don't yet own one. The manual works best when you have the treadmill in front of you, and you work side by side with the manual.) Therefore, the best time to get educated about how to deal with your spouse and your children is when you actually have a spouse and children. The classes on these things should be AFTER one is married.
In addition, there should be someone you trust and respect with all your heart and soul that you can talk to about marriage issues. After all, every issue requires its own unique remedy.
There are far too many pathetic idiots who believe that after being disrespectful and unsympathetic to their wife for an entire week they can bring home flowers on Friday and everything will suddenly sort itself out. First, not every woman likes flowers on a weekly basis. Second, flowers will not remedy the problem of you being an idiot and not helping around the house.