Spammers are blocked from the site by username and/or IP address. If they keep coming back from different locations, they may be reported to their ISP and/or appropriate law enforcement if the situation warrants.
A spammer is a person who asks stupid questions that are no meaning whatsoever, For example "Do your mom know?" or something like that. So they are spamming the site, or they go in and answer...
When you click on the red "report abuse" option on the top right side of the question and answer page, it sends the report to the appropriate people who will investigate it for obscenity,...