Wait in line for the class. They only have X amount of seats available per class. They do have a sample out front usually of who you are drawing. I have no art skills, but they break it down to pretty simple instructions. As someone that has no clue I am just following their lead of circle here, line there, etc... & suddenly at the end it all comes together to be something which is pretty cool!
As a sidenote you then have to carry your artwork all day so be ready for that. In the past I have used a plastic bag to lay the drawing flat inside & then rolled it around a water or Gatorade bottle & tied it with a hairband to put in my backpack. Not the best method but it made it home somewhat safe & I was able to hang it on my fridge.