Well, you could fire up Dreamweaver, hit F1 (Help), and in the search tab, you can enter 'site' or 'definition'.
Alternatively, after hitting F1, goto the contents tab, then select 'Dreamweaver Basics', then in the dropdown select 'Setting up a Dreamweaver Site', and in that dropdown, finally click on Reference.
Here, you will find info on Site Definition setup.
Cheers,
NRG