Dblinks are a start...
Have you thought about using snapshots (v8) or materialised views (8i,9) to do this as well....depending on whether you want the whole table or even schema replicated.

All that is needed for a database link is to have a valid tnsnames alias to point to either db1 or db2.
The Oracle documentation on links is good and explains the concept well.

Why i suggested replication via snapshots or materialised views is once this is setup Oracle can manage the whole process via job scheduling.
Does the requirement for the application require a loan record in one database (db1) be replicated in database (db2) if so, i suggest reading the chapters in the documentation on basic replication. You already have the building blocks (primary keys on all tables) and the same schema name, so setting this up will be straightforward.

Have Fun