First you have to get the IP address, so find a post by the user and in their Profile bar thingie on the left, hover over the blue and green icon (to the right of the online status, reputation and report icons)
Type that IP address into Google. It'll return a bunch of trace pages, and usually most will tell you where the IP address is from, so it's nice to see that a user from NJ has an IP address from NJ, doesn't always work that way because of proxy servers, but it's nice confirmation when it happens. What I look for is any link to a result on a "Project Honey Pot" site. If it tells you that address has been reported for spamming or other unauthorized activity, then I report that IP and User name on the CG Support thread. They'll ban the IP, but not the user. If we see infractions we can go ahead and also ban the user. we had one where they switched IPs after an IP ban, so we kind of have to wait for them to infract beforce user banning.