The best place to start here is ANYWHERE! Just jump right in! You've made an excellent choice by joining the 500. There are great benefits (check out the Writer's Digest discount!) and new things are added all the time.
Just a warning, though: These message boards can become quite addicting. You might want to limit your intake to checking in once every hour or so.
On the other hand, you'll meet some great friends, get wise advice from old writing pros (not necessarily old in age!) and you'll be encouraged, lifted up and blessed here. You might just want to grab a pot of coffee and stay all day!
See ya around!