Take this scenario:
Suppose the customer has no backup of Oracle 9i or 10g database. The customer wants to move the database from one PC to another. The other PC has a fresh installation of Oracle.
How to move the data and other files and attach to the new installation? In this scenario, we don't have any type of backup, neither a dump nor any other type.
Make a backup and restore it to your new Pc and make backups in the future!
Check out this SF question.
The exact way, could depend on your configuration, but roughly, you could:
1) Export / Import (see documentation for exp)
2) Cold backup:
There are some steps to do in between, but the advice is to consult with an oracle DBA, or read the documentation on otn