Welcome to bitcointalk.org and hope that you'll have a beautiful experience in this forum. For Rank system you have to see the meta for details, but if you want I can tell you something about rank.

There are 8 rank in this forum.

Brand New (When you sign up in this forum)
Newbie (When you make at least 1 one post)
Jr Member (When you reach an activity of 30 points and 30 messages. Activity is determined from time that you're logged in and messages that you do here).
Member (60 activity points and 60 messages).
Full Member (120 activity points and 120 messages).
Sr. Member (240 activity points and 240 messages).
Hero Member (480 activity points and 480 messages).
Legendary Member (960 activity points and 960 messages).

If you want more information, go to meta section.