Hi Sri,
When you join this site you are allocated the title "greenhorn".
After you have posted 30 times your title is automatically changed to "Ranch Hand".
Bartenders are nominated by current sheriffs/bartenders based on their helpfulness around the ranch. They usually moderate one or more forums, and can move posts from that forum or edit them if necessary. They also help with general work around the Ranch.
Sheriffs are appointed by the trailboss,
Paul Wheaton. They have the power to act as bartender in any forum at any time.
Paul Wheaton is the owner of this site, and as such he has the special title of "trailboss".
Those people who have written books are given the title "author", and are given access to an authors only forum where they can discuss whatever it is that authors discuss.
Most of the other titles you see are "vanity" titles - they are offered to those people who
make a donation to keep this site running.
Regards, Andrew