This function is only available when connected to a Teradata database.
The random function is a non-standard Teradata SQL feature, generating RANDOM (x, y) and returning a pseudo-random integer between x and y. When dragging a Random into a variable, the following tree element is created.
The integers x (Lower Bound) and y (Upper Bound) are set through the Properties panel. Double-click on Random, or highlight it and click Properties.