passwd

Can anyone tell me how to set passwd for users? I do
what I told in pg_passwd man it doesn;t seem to work.
eg, when I do
psql -u testdb
UserName: user
password: ....

anything i type in password let user access testdb,
I beilive that this username and password are what we have to
put in jdbc getConnection? Am I right?

one more question if one user create db is this accessable from
other users? Seem to me it si now since my authentification is not
working .....

Thanks
Katsu