The input for Condition and Not nodes must be a Condition output or a conditional expression. A Condition node is true when the specified condition evaluates to true. A Not node is true when the specified condition evaluates to false.
When a Condition or Not node is added, a small dialog appears:
This dialog allows you to enter a conditional expression (an expression which evaluates to true or false), or create a link to a condition-type output of another GoldSim element.