I’ve been a DM for many years, and in all that time I’ve had maybe three players read the PHB. I don’t mind explaining the rules, but it would be nice to not have to remind the wizard how spell slots work (again). Is this a common thing for most groups?
When I was maybe 8 or 9, my dad offered to teach me to play D&D.
I told him I wanted to be a wizard, so he told me I had to memorize every 1st level spell in the AD&D 2e PHB before he’d let me make a wizard.
I had them down cold in a week.
If your players really want to play, and you want them to improve, talk about it with them. Don’t nag, just set the standard that they need to know how everything on their character sheet works. If they can’t do that, their character can’t remember how to use the feat/skill/spell/item in question at the moment.
Of course, if there are exotic interactions between effects, that’s on the GM to resolve. Likewise you should make some exceptions for edge cases, but spell slots? Come on.
At 8 or 9 you also had a lot less on your plate than a group in their 30s / 40s.