I need to resolve the question

What would be the first thing you would do if an end user complains that performance is poor

check server hardware and oracle instance memory with operating system memory diagnostics

check database from EM is there any critical error tablespace full
what the users are doing consumers ..etc
so many thing you can get from EM
from the sever also status bar RMA& CPU

check with the end user what is the function has bad performance and try to trace his session to see if there's a query with a bad performnace
and if you working with oracle 10g you can use EM create an ADDM report to see a detailed report for the dataabse behavior during this period
hope this will help you

جزاكم الله خير.