A few books have been written on Gambas.
Some documents you should read to get started with Gambas.
The answers that everyone always wanted to read.
Gambas is "libre" software, i.e. free software. But, be careful, "free" stands there for freedom, not for price!
This Wiki made by myself is hosted by Rob Kudla. It is the center of every documentation on Gambas.
If you are spanish, see also the castilian/spanish Gambas web site.