The Announcements module has built-in Read More functionality, which allows you to put together a big article and then display just the first few lines followed by a 'Read More' link. The nice part about that is that you don't have to manually cut your article up into the teaser and full text views - the Announcements module does that for you.
If you're looking to do this in HTML, I think you would need to put your teaser text into a regular Text/HTML module and then put the full text onto a separate page that you then link to.
I can also tell you that there are other Announcements-like modules out there (DigArticle by DigNuke(
http://dignuke.com), for example) that provide more flexibility for automatically breaking up your text into pages, etc.
Hope this helps.