Hi,
I believed you configured OEM in your system after the installation, before asking this query.
If not, then you need to configure it, As far as I can recall, it was delivered with the package itself in my 10g oracle, just a configuration was required with correct user and it's service was working fine.
Make sure you use OEM carefully, as it I have seen people killing databases with OEM and TOADs.
However, just for monitoring and for things like adding datafiles, it good.
Regards