Are there any prerequisites for joining a class?

There are no prerequisites for beginners. 

Mind you, when starting a class, it is normal to feel a bit lost. This is part of the process. It is important to just follow along at this stage. You will notice that after a few weeks you will notice a class pattern. So just enjoy the process and don't be too hard on yourself. 

However, advanced classes may require prior experience or approval from an instructor. These classes are conducted with the assumption that you have covered the basics and have the right co-ordination and skill level as expected. As for the beginners, each teacher will have slight variations in teaching style, methodology and pacing. This is normal and expected.