This is a fairly new feature, and one that questions have been asked of a few times, so I'll attempt to explain it.
Thanks to Paddy for the donor post
The green bars are an indication of a users reputation. Similar to 'Likes' facility, reputation is gained (or lost) by clicking the star highlighted at the bottom of each post. A positive repuation can just be left, a negative reputation involves leaving a comment.
You can see where your reputation has come from by clicking on 'Settings' in the top right of your screen.
Thanks to Paddy for the donor post
The green bars are an indication of a users reputation. Similar to 'Likes' facility, reputation is gained (or lost) by clicking the star highlighted at the bottom of each post. A positive repuation can just be left, a negative reputation involves leaving a comment.
You can see where your reputation has come from by clicking on 'Settings' in the top right of your screen.