Oracle Databases - need to export nightly for backup/DR purposes
if your database is a serious production database, it should be running in archivelog mode, no question about that. This is assuming that users are constantly doing transactions and that you don't want to lose them. If your database is only bulk loaded once a day, an export dump might be a valid solution as backup, if you know how to use it to re-create a new database, once you lost the prod database.

For now, logon as a database administrator on your server and switch to archivelog mode


sqlplus / as sysdba
shutdown immediate;
startup mount;
alter database archivelog;
alter database open;


database is open for production and you can make online backups. This does not mean your database is out of the danger zone, there are still a few things that need to be setup to keep it running without problems.

First thing that will happen is that the filesystem where your archivelog files are written will get filled up, causing a full halt of the database.

best advice: hire a dba to do the job for you, it is easier to make a disaster than to prevent, or even worse, to recover from one. Without the proper config recovery can be close to impossible. There are lots of consultancy firms that offer adhoc services via some pre-paid system. Maybe giving the application to a service provider might be smarter. This al depends on what you do and what kind of protection against disaster[s] you want.

second best: start reading the docs Oracle® Database 2 Day DBA