Give reputation by clicking the "Mark as Helpful/Unhelpful" link at the bottom of any post.
You will be prompted to select a reason for giving the reputation from a list. This is to ensure that the reason for giving the reputation point is legitimate, as well as so that the member receiving the point knows what they are doing well, or need to improve on when posting. Note that if you cannot find the reason for which you wish to give someone reputation in the list, it may be better to report the post or contact a moderator via Private Message.
After filling out the information, click Add To Reputation to have the point added to the recieving member's profile.