It depends on what you are doing... You will always have the standard descriptors when creating J2EE components:
application.xml for Enterprise Applications
ejb-jar.xml for EJBs
web.xml for Web Applications
Each J2EE component also has a WebLogic-specific descriptor that may be optional...
weblogic-application.xml for Enterprise Applications
weblogic-ejb.jar.xml for EJBs
weblogic.xml for Web Applications
For server configuration there is the config.xml... though this file shouldn't really need to be touched by hand. Occassionally I'll edit it outside of WebLogic but you really need to know what you are doing or you could easily hose your system configuration and never, never edit this file while the server is running.
I got this tall by not having enough crisco in my diet as a kid. This ad looks like it had plenty of shortening: