These suffixes are often given when a son is named after the father. Example: John has a son also named John. Dad is John SR., son is John JR. Or John I and son, John II. Now if John JR (II) has a son named John, he would be John III and so on. Hope I didn't confuse you any more.
A suffix is a part of a word that is placed after an initial word. An example of a suffix is the word helpful, in this word help is the initial word and ?fuly is the suffix?. http://www.cpearson.com/excel/firstlast.htm