Is it a beginners class or an advanced class? At the beginners class they teach you how to ice a cake, how to pipe a border, how to make roses, and how to write on a cake. Warning: If you have hot hands, you'll have a difficult time making roses. At the end of the day, you should be able to decorate a basic cake. How long the class is depends on how many people are taking the class, how many instructors are there, and how fast everyone catches on.
It's a beginner's class. I've worked in the bakery for about 9 months and so far, all I can really do is write on cakes (and even that's not that great but it's good enough no one's complained, lol). There's another coworker who's been there for about a year and she's going too though.