The manual for the latest stable version is available online:

• User's manual
• Class library reference (part I - base classes)
• Class library reference (part II - other)

You can also search the contents of this site, browse the GNU Smalltalk Frequently Asked Questions, or look up the information you need in the wiki (e.g. the examples page).

If everything else fails, other users may help you on the mailing list or on IRC.

Books

There are many free books about Smalltalk. While not specifically targeted towards GNU Smalltalk, they can be an extremely rich resource for anyone wishing to learn Smalltalk or object-oriented programming.