Hi NatashaGregg,
Thank you for reaching out Microsoft Community.
Please utilize this link>>https://support.microsoft.com/en-us/help/4023496/surface-troubleshoot-connecting-to-a-second-screen to get some of the information you need to consider when extending your Surface display to external monitor. For Surface Book, you can extend its display using a mini-DP port adapter but if in case you'd like to extend it while using it as a tablet, you'll be needing a Surface connect cable and a Surface dock to get it to work.
If this answers your question, please feel free to mark this post as an answer. Otherwise, don't hesitate to respond to this thread if there's anything else that needs to be addressed.
Kind Regards,
Crest_Z