Subchapters:

Syntax

Commands and functions have parameters and keywords. The keywords are named in the calling sequence:

IDL> plot,x,y,xrange=[10,1000],color=5,/ylog

Here xrange and color are explicitly set to their values.

The ylog keyword is boolean (if = 1, the plot will be in log scale on the Y axe, else linear scale will be used).
This can be specified by ylog=1, or shortly by /ylog.

Keywords can be abreviate:

IDL> plot , x , y , xrange=[0,200]
IDL> plot , x , y , xr=[0,200]

are equivalent.

The help can be called from outside idl, under Unix, by idlhelp, or within an IDL session, by:

IDL> ?

This help is a Hypertext manual pages and most of what you need is inside.

If you need information on a variable (like: is toto a double precision real or not?), you can examine it by:

IDL> help , toto

When you are finished:

IDL> exit