How can i know the relationship in the database in sql server 2008?

I want to know how can i know the relationship in the database which is not determined by the primary key in the design

for example i have three tables in the database following like this :-

table 1 : fields table 2 : area table 3: location

and all of the tables have data but who created database did not explain the primary keys and the foreign keys in it , so how can i know the relationship between this tables ?

note : i using sql server 2008