Currently with 11.5.8-9-10 or may be previous versions you might be using 9i Application Server Version 18.104.22.168.2 . As you are aware 10g Application Server 10.1.x.x as well is now certified with Oracle Applications 11i , I think its quite important for you to learn 10g Application Server basics as well.
P.S. For Oracle Applications 11i newbie or new Oracle users 10g Application Server is different from 10g Database.
10g Application Server is also important because with next Oracle Applications E-Business Suite Release (Which I assume is going to be named as R12 ) is coming with 10g Application Server replacing current 9iAS . (This is for information purpose only) 10 g Application Server is also important because of Oracle Internet Directory & Oracle Single Sign-On ( OID & SSO ) features. As I have been working on 10g Application Server with its first release as version 9.0.4 I thought of sharing this knowledge with you in my second blog (I'll update it once a week most probably on weekends ) with basics & where to find study material & what you should read w.r.t. 11i & 10g Integration .