You will see the oldest related record. Note that what constitutes the oldest record can be changed if you sort the records and then import them into new copy of your file (when you're updating your solution or replacing a recovered/damaged file for example.)
sorry but i dont get it.. i am not importing so if the values exist in the system then what shall happen???
The first such related record to be created. Say I create 2 records with that match--one in the morning and one later on in the afternoon. The one created in the morning is the one I will see. You can check this by finding all the matching records and choosing "unsort". The first record in the set is the one that'll supply data to your layout via your relationship.
What I wrote about importing is to caution you that which record is treated as the "oldest record" could be changed if you ever need to move your records via import into a different copy of your database. This is a fairly common procedure to do at some time during the life of your database, so be careful if you do.
You might want to modify the design of your database so that you don't have to rely on this.
... i.e. are they sorted by any specific value??
They aren't but you can sort the relationships by any value that you wish.
Go to the Relationship Grafh, double click the join symbol and, into the new window check the sort button on the side of Contacts.