Newbie Needs Help With Hyperlink Code

I am trying to create a hyperlink from other values in a number of fields, I have found a thread which I think anwers my problem:

Link to Thread (http://www.access-programmers.co.uk/forums/showthread.php?t=124117&highlight=hyperlink)

Only problem I is I don't really understand it. :confused:

e.g.

Dim stGunlib As String
Dim stGunlib2 As String

stGunlib2 = Me![Stock number]
stGunlib = "#http://www.shooting.uk.com/Gunlibrary/" + stGunlib2 + ".jpg#"
Me![Link] = stGunlib
Me![Picture] = stGunlib

What does Dim, Me!, As String mean? and where would this code be entered, is it part of a module or just in the properties of a table/form etc?

Any help on explanations of this would be greatly appreciated!