I've looked everywhere I could find on the site and can't find where it is explained.
Thank you.
Once you get 50 posts, you gain a rep power. For every certain number of posts you make, you gain a rep power. Eventually the post number doubles so it'll take longer to get a power. Rep comments also gain you a power, and you gain rep points based on how many powers the person repping you has. For example, you'd gain 110 points if I repped you. For every year that you're here, you earn 1 rep point. In addition to getting rep points, you also gain green bars. Eleven bars seems to be the maximum number you can get.
To give a rep comment, click on the star icon at the bottom left of a person's post. You can either leave a comment, or just your name. I usually leave my name as well as a comment because most here like to thank whoever gives them rep. Right now YOU have no rep powers, so if you do rep someone, they won't gain a power. You need to get 100 rep points to get a power.
Hope this helps you.