Reputation comments are a bit of fun really. If you see a post that you like or someone gives you support you can add to their reputation. You will see people's reputation scores under their avatar. To add to someone's reputation you select the middle symbol at the bottom of their avatar looks like a set of scales.
Hope that helps, think there is more on it in the Technical forum.
Rep points can be given to you by other members for a post you make on any thread. It is activated by clicking on the middle icon of the 3 that are at the bottom left of every post. You are given an option to approve/disapprove a post and then type a personal comment to add to the rep point.
Hope this helps to explain. Please come back if I have made it as clear as mud....lol