In order to write code, you need to understand the basic principles.
If you already know other programming languages, then you know some of these concepts, but watch out: REBOL is different in many ways. So, it may be good just to scan these over.
Learn the code: basic syntax of the language. It's different in important ways.
Please read code: evaluating blocks, because code is data, and data can be code.
It is essential to understand the code: words and variables.
The key to code is to know code: how code is evaluated including operator precedence.
Learn about code: conditional evaluation used for functions like if, either, case, switch, and select.
For iteration, read code: repeated evaluation (loops) about loop, repeat, for, foreach, forall, while, and until.
And finally, you'll need code: defining functions to build any serious programs.
Of course, there's quite a lot more to on this topic, which you can find in the Expressions section.