You may specify what information is to be displayed by adding arguments and/or keywords. If some keywords (e.g., system_variables) are used arguments will be ignored. Here are a few of the more common ways to use HELP:
gives a one line description of each variable listed,
gives a one line description of each open file listed,
help,/sys shows all system variables and their values,
shows the contents of each structure listed (e.g., system variable !P).
Only one keyword may be specified at a time. Positional parameters are optional. For example, help,/files will list all open files, and help,/struc will show the contents of all currently defined structures. See the IDL User's Guide for more information.