Read all about those green bars
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.
You can also give rep to someone by clicking the green flag
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in the top right of someones post.
"I approve" = +rep
"I disapprove" = -rep
If you're going to -rep someone, you HAVE to give a reason as to why. Also, you have the option to leave a comment for a +rep, but it's not required.
One other thing :3. You can Thank a post
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. You can only thank a post to the original poster. (Person who made the thread) This gives the person +5 rep points. Meanwhile giving someone rep through the green flag method gives a person rep depending on your rep power.
In case you don't understand rep power I'll explain it to you because I didn't understand it when I first read it xD.
This means, when someone first makes an account. They have the ability to +rep someone and give them 1 point towards their reputation power. But for every year that you're here, you then gain another rep power, giving you 2 points instead of one. The same thing applies for every thousand posts and reputation you get.
For examples, say you've been here for 4 months, you have 6,200 posts, and 1350 rep.
If you +repped someone you'd give them +8 to their rep power. If you -repped someone you'd give them -8 to their rep power. Meanwhile if you Thank a post, you'd give that person +5 rep power.
Hope I helped :3