A process server is someone who is trained to serve legal documents. Different types of documents can be served in different ways. A process server knows all the rules of service and determines the proper way to deliver the legal documents.
Once they serve the documents, they prepare all the necessary paperwork required to prove to the court that the legal document was served. This is called an Affidavit of Service. If the process server makes several attempts to serve a document but is unsuccessful, they will generally provide you with a document called Attempted Affidavit of Service. This affidavit can be used to assist you in obtaining an order by the court to serve the document in a different way, not normally permitted by the rules.
Most process servers will attempt to serve the document at varying times of the day and on weekends before they close their file. This is important if the legal documents do not get served and you need an Affidavit of Attempted Service, as the court will want to know that you have tried at appropriate times of the day.