If you want to add extra information that is not critical to a sentence, the information should have a comma before and after it. To test if the information is critical to the understanding of the sentence or not read the sentence without it.
- Audrey, who is very tired, is going on holiday next week.
(The commas before and after who is very tired are needed because this information is not critical to the sentence.)
Audrey is going on holiday next week.
(With the information deleted the sentence is still understandable.) - Our hotel, which only had eight rooms, was fantastic.
