A very simple plot using three arrays

Try,

window,0,retain=2
x=[1.,2.,3.,4.]
y3=x^3.

plot,x,y3
y2=x^2. 
oplot,x,y2,linestyle=2

Note that the deafult is white on black. You can change this with

!p.color=0
!p.background=256*256-1

``!p.'' in IDL is always used to change the default value of something.

x,y and y3 are arrays of numbers. Arrays are just single variables that contain lists or multi-dimensional grids of numbers.

You can easily refer to indiviual elements of an array using, for example,

print,x(1)

Note IDL counts from zero!

Or several elements,

print,x(0:1)

Or all elements

print,x(*)

``*'' is most useful when you have a multi-dimenisoanl array and you can use ``*'' refer to a whole row or column etc. For example

a=[[1,2,3],[1,2,3]; create a 2D array
print,a(0,*) 
print,a(*,0)

You will spend a lot of time messing around with arrays of numbers and plotting them using IDL during your PhD and we will return to them later.