The recipe is written in Twee Notation and is basically stating:
1. Add a new Passage to your project, name it Typewriter and place the following code within this passage.
<!-- Create a variable to track the position within the $typewriterText string -->
(set: $typewriterPos to 1)
<!-- Create a hook to hold the typed text -->
<!-- Set a delay of 20ms seconds per loop -->
<!-- Add the next character to the hook -->
(append: ?typewriterOutput)[(print: $typewriterText's $typewriterPos)]
<!-- Update the position -->
(set: $typewriterPos to it + 1)
<!-- If it's gone past the end, stop -->
(if: $typewriterPos is $typewriterText's length + 1)[
2. Within the Passage of your project that you want to see the typewritter effect in use the (set:) macro to create a $typewriterText story cariable, then assign this variable the Text you want to the typewritter effect to display. Once you have done that used the (display:) macro to execute the code contained within the passage created in point 1.
(set: $typewriterText to "Hello, world!")
When you view this passage of your project using either the Test or Play option the text contained within the $typewriterText should appear using the typewritter effect.