To learn IDL, there are many good tutorials on the web, or you can start with our local tutorial, idl_intro.html. A second tutorial, Using IDL for more advanced Plotting, is also available, and shows how to read MDSplus data from NSTX ot NSTX-U into IDL.
There is an excellent demo supplied with idl, which shows many of the advanced things IDL can do. Just type "demo" at the IDL prompt. The source code for these demos is often a good place to start when building your own application.
Hardcopy documentation is no longer sold by the IDL company. The on-line help is pretty good, but you may wish to download the various PDF files comprising the full documentation set. You may find these somewhere on the web , or on the PPPL "P:" drive: On a PC, double-click on "My Computer" and navigate to "P:\departments\Engineering". The files are in the folder named "New Folder" as of this writing, but may have been renamed.
You may also want to look at the IDL-supplied examples in $IDL_DIR/examples on Linux.
There is web-based help on user-written routines used at PPPL. If you want to run from a standalone computer, these routines and others can be downloaded individually, or from a tar file.
You should also visit these valuable IDL sites, especially the ones that let you search for IDL routines written by others.