Flagging others and downvoting

I don't do this enough. There is a reason. The one time I agreed with myself that someone needed to be flagged and downvoted, because he is causing so much damage to the network - I DID NOT KNOW how to do it! And that person is still rampaging along, doing his thing.

Can someone PLEASE show us once and for all how to downvote someone?

PS: I'm gonna feel real stupid once I figure out that it was tooooo easy... it's worth it!