Please treat your fellow members with courtesy and respect. They will be attended by members with a wide range of skills in the area under discussion. SIGs meetings are always free as a part of your membership. Classes are formal hands-on instruction sessions attended by members with a basically uniform level of experience. There is generally a minimal charge for classes to cover the cost of instructional materials.
Classes generally fill up very quickly so sign up well in advance.
I attended a SIG and they talked way over my head. But even if they don't, go ahead and attend and listen carefully. You will learn a lot. It is similar to learning a sport. You learn quicker and faster if you play competition at a higher level than yourself.