To have the OEM working you have to have a repository created in one of your instances ... To create the repository use.

$ emca

Then start the management server as

oemctrl start oms

Once you start it, you can connect to it as

lsnrctl dbsnmp_start <-- start the intelligent agent
vppcntl -start <- start the data gatherer

oemapp console

username: sysman
password: oem_temp
host: your database server name

If you have any problem, please let us know of the error message and the problem...

Sam