How to connect using a key field one dataset to another.

I am new to this so I hope this makes sense. I am creating a new site. I have a obit dataset and a guestbook dataset. Each has different fields. I want the capability to use the deceased name from the obit dataset as a key to the guestbook dataset. The purpose is when the user goes to the guestbook page I don’t want them to retype the deceased name - I want the name to appear.