If you want to add extra information that is not critical to a sentence, the information should have a comma before and after it. If the information was deleted the sentence would still be understandable.
- 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 for 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.
