英语句式问题.Prior to her marriage , my mother was a nurse. 逗号前是作状

英语句式问题.
Prior to her marriage , my mother was a nurse. 逗号前是作状语吗?这个逗号怎么用?什么时候用?
还有像这句：The house , of spanish colonial design, has rooms with graciousness of proportion and beautiful details.
就是那个逗号问题,什么时候用,代表着什么呢,应该可以转化为造价的带有引导词的句子是吧,像非限制性定语从句那种.谢谢