Oracle Projects Add Assignment no person

Hello Folks, On the project web page,I am trying to add assignment under resource tab. System is already setup and i was not involved in that. In the person field i can see only one employee(somehow Its default whatever role i select). I want to add some other resource in the assignment but i am not able to see that. I have even tried to create a new role and assign that resource job to this newly created role but no luck. Could you please suggest what are the various validation criterion to see the resources under this person field?