Yo Quiero / Quisiera / Me Gustaria - ???
So the Latin American Spanish I have learned has been telling me to use "Yo quiero" when I want something but I have just found out this is not very polite.
Apparently I should be using "quisiera" or "me gustaria" instead. But I am confused what they actually mean and when I should use them.
Also do I need to use "yo" as well;
"Yo quisiera una manzana" or just "quisiera una manzana"