Check out the Menu choices above. Each leads to a different section of the site.
Category: Sheet Worker Guide
Undefined and Other Error Values
A short noted about undefined and similar "unvariables". Avoid them when you can.
Strings, Arrays, and Loops
An example of using different techniques to solve a problem - Strings, Loops, and Arrays.
Strings in Sheet Workers
Introducing the concept of Strings, what they are and you use them in Roll20.