A process server does not need to be licensed in every state. A process server must be licensed in Alaska, Florida, California, Illinois, Montana, Nevada, Oklahoma, Washington. There are some states that have local licensing requirements as well. For a more details on local and statewide licensing laws for process servers, please visit the web sites for National Process Server Associations page.
What is a writ?
An official court document, signed by a judge or bearing an official court seal, which commands the person to whom it is addressed, to do something specific. That "person" is typically either a sheriff (who may be instructed to seize property, for example) or a defendant (for whom the writ is the first notice of formal legal action. In these cases, the writ would command the person to answer the charges laid out in the suit, or else judgment may be made against them in their absence).