"Will all my friends and family be able to see that I'm in this group and what I post or react to?"
NO! The group is "private" which means that only other foreign-trained professionals who are in the group can see the posts and activity.
"Do I have to pay?"
NO! It's free for you to join.
"What are the trainings about?"
A variety of topics: TOEFL iBT Writing, Reading, Listening and Speaking... grammar... pronunciation... as well as how to deal with your stress or anxiety in the most effective ways so that you can focus during the exam (and at home while studying) and collect the most points.