On Linux system, there should be such lines in your ~/.cshrc file:
source /usr/physics/idl8/idl/idl/bin/idl_setup
setenv IDL_PATH $IDL_DIR/lib:/yourFullPathIDLsourceCodeDirectory"
the second line sets up search path for IDL procedures. $IDL_DIR/lib refers to the place for IDL built-in procedures. /yourFullPathIDLsourceCodeDirectory refers to the directory for IDL procedures you have owned, eg. $HOME/IDL
On window system, to set additional search path for IDL procedures, do as follows, after starting idlde,
on top of idlde window, select:
File -> Preference
A separate window pops up, click tab Path, then click Insert
Select a directory to be added to the IDL search path.
To set your working/current directory after starting idlde, do as follows,
on top of idlde window, select:
File -> Preference
A separate window pops up, click tab Startup, enter for Working Directory
/fullPath4yourWorkingDirectory
Then click OK