refer to online tutorials, there are plenty around,
When I was learning GWT, i was refering to
http://examples.roughian.com/
good site giving precise information about every element in GWT, however as now GWT 2.0 is now released,
most of the examples there are outdated, however, i still feel
you should refer to them.
The showcase source code is also a good reference to begin with,
you need to know basic HTML and CSS knowledge to get started with the behaviors of the widgets.
GWT is really an amazing technology.
- GWT Fan,
Salvin Francis.