Any website that teaches BASIC is probably not going to be enough for you to use DarkBASIC. It will just include commands like Print, For..Next, If..then, etc. The help files for DarkBASIC are comprehensive enough for you to learn what you need. If you only have the demo, here is a brief list of what the full version help includes:
INTRODUCTION
-Not much here
GETTING STARTED
-Interface info, how to install, etc.
PRINCIPALS
-Commands/terminology common to every programming language
COMMANDS
-Every command available in DBPro, organized by category, with brief descriptios
EXAMPLES
-Usable examples of code demonstrating a particular procedure, very useful.
TUTORIALS
-Exactly what it sounds like. Covers a decent amount of functionality
INDEX
-Every command listed in alphabetical order.