Creating database and wish to automate

I have been working on a database (for a really long time) and getting
nowhere. I am stuck on how to get data in a field from one table into
another. Specifically- I have a table listing patient demographics in
separate fields (MR#(Key), Last Name, Address...). The next step is to go to
a table (Relationship is the MR# field) that l list each hospital episode
data (admission date, diagnosis, physician...). There can be many hospital
records for each patient. I am currently stuck at the point where I would
like to enter the MR# on the hospitalization table and the last name and
first name from the demographics table automatically fills in when the MR#
match. As soon as I get this down, I am sure I will come up with another
issue, but I have to start somewhere. Thanks, Theresa