In most cases Documentum set up to Linux/Unix environment - RHEL/AIX distributives (though Windows version of DCTM is included), so you need to be experiencied in *nix command.
If you are developer, in a nutshell, you are doing the next points
1) For files (content) processing - write methods (classes) for Java Method Server
2) For GUI - customize java web-applications (Taskspase or Webtop)