>I am new in this field and preparing for an 10g OCA DBA exam
So what you are saying is that you want to become a DBA, but you can NOT figure out how to even log into the DB.
I am correctly understanding the situation?
My crystal ball is in the shop for repair.
I wonder why you think we could answer your questions when we have no idea what you've actually done on YOUR computer or even if you have Oracle database s/w installed.