Ubuntu installed postgresql password failure

I have reached my wit's end.  lol  I installed postgresql (9.3.9) and
pgadmin3 with the Ubuntu Software Center.  When using pgadmin or psql, I
get an error "password authentication failed for user "postgres" ".
Ubuntu (14.04.3).

I created a postgres user BEFORE installing postgresql/pgadmin toolset.
The password I used for the postgres user will not work with the
installed postgresql tools.

What in the world am I doing wrong, and more importantly, how do I
determine the password used for postgres during the postgresql install?
AND, why should it be different from the postgres user I created.

Any help will be greatly appreciated.

Dale