There are 2 reasons to get increased and decreased of the value of your reputation.
1.Saying Thank you (merci)
:- When u posting a new topic , u got this chance.You can thank 1 of the people who comment on it (only 1 per new topic).And his Reputation will get +3. The merci button will only appear for your new posts (not comments).
:- We can see a (+) mark and a (-) mark in each comment. It's on the right hand side upper corner. And if we vote (+) for someone's comment , he will get +1 reputation and works same in (-), if someone vote (-) for his comment, his reputation will decrease by 1
Simply (+) vote = Increasing his/her reputation by 1
(-) vote = Decreasing his/her reputation by 1
And that's what i found on the reputation system here. Using those for good will make this place better.
Moderators correct me if i am wrong.
Use this system for good.