A star is added beneath your name as you go up in "rank". So since you're still new, you only have one star, but as you continue posting your rank goes up when you hit a certain number of posts. So you earn a number of stars depending on what rank you reach :3
Here's a list of the ranks you can get, how many stars each one has, and how many posts you have to do to reach them:
Newbie * 0
Jr. Member * 25
Sr. Member ** 50
Experienced Member ** 100
Dedicated Member *** 250
Full Member *** 500
Elder Member **** 1000
Elite Member **** 1500
Hero Member ***** 2500
Legendary Member ***** 4000
Source of list can be found here:
[link]Hope this helps!