Well, first you should read the [url=http://doc.silverstripe.org/tutorial:1-building-a-basic-site]tutorial[/url].
The not-so-nice approach is to simply check the page name in the template:
<% if URLSegment = whateverpageurl %>
<% else %>
<% end_if %>
The better approach is like it's described in the tutorial:
- Create a new page type
- Rebuild Database with /dev/build/?flush
- Reload the CMS and change the page type of this particular page
- Replace '$Content $Form' to '$Layout' in Page.ss
- Make a new Page.ss in the Layout folder
- Add '$Content $Form' into Layout/Page.ss
- Make a new [whateverclassnameyouvechosen].ss in the Layout folder
- Add '<div>$Content $Form</div>' into Layout/[whateverclassnameyouvechosen].ss
- Reload the webpage with ?flush in the end of the URL.