A concurrent request is a process or set of processes which call a concurrent prgram. It is important for an Apps DBA to know what the most critical concurrent processes do on code level. That means opening the sql files or unix shell scripts and understanding what is happening in a concurrent program. If you understand the program on a high level, it will help you in troubleshooting any issues with concurrent requests which call that program. An exmaple of a high level knowledge is this: The program checks some conditions, with select queries, then it loads some data thru SQL*Loader which goes to some interface table. Then it further checks some more conditions and inserts data in staging tables. If you know this much, without actually going into further details, it should be enough to give you clues in case a request calling the program seems to have hung.
Some Metalink Notes which have scripts for analyzing pending requests and analyzing a single request:
134033.1 ANALYZEPENDING.SQL - Analyze all Pending Requests
134035.1 ANALYZEREQ.SQL - Detailed Analysis of One Concurrent Request (Release 11 and up)