As the FAQ has said, each member (you) helps to moderate the community. When a member gains enough reputation, he or she can do almost anything a moderator can do. Votes help to manage reputation, when you down-vote you are to down-vote only the low quality, and of course give a comment to say the reason of your down voting. Up-voting gives reputation, and up-voting should only be for high quality posts.
Voting incorrectly can result in someone irresponsible and undeserving gaining powers, and a deserving person losing powers. So up-vote only the high quality posts, if it deserves a down-vote give it, don't give a down-vote deserving post an upvote out of sympathy, if you do, than that is one step towards a bad site. Down-vote only the posts deserving down-votes.
So this is how voting works, which either gives or takes reputation of a user, which also gives or takes moderator abilities of a non-moderator. Please understand that moderators are no different than users.
Please check out the FAQ: http://forum.islam.com/faq/