In this example:

where A.object_id(+)=b.id1

It will include all records which fulfill the join criteria AND all records from table b but no matching record in table a.

i.e. It marks which column can have null data corresponding to non-null calues in the other table

or
where A.object_id=b.id1 (+)

Will do the otherway round - all records matching the join, + records from table a which aren't in table b.

e.g.
select a.dept, b.employee
where a.deptid = b.deptid (+)

could give (departments without employees):

DEPT----EMPLOYEE
1a-------SMITH
2b-------JONES
3a-------

or say to find out which employees don't have a department:
select a.dept, b.employee
where a.deptid (+) = b.deptid

DEPT----EMPLOYEE
1a-------SMITH
2b-------JONES
----------MURPHY


Hope that helps,

Terry