Custom variables are not built into Setup Factory - instead, they're created whenever you specify a new variable name to receive a value.
Custom variables can be used to receive user input, such as the user's email address or phone number. They can also be used to receive information from the Registry or INI files, such as the path where a given software component is installed on the user's system. For instance, you would use a custom variable when you query the Registry for information that was put there by another application.
You can even make the way your installer operates depend on the values of specific variables. Using variables, you could install different files if a certain registry key exists, or skip a screen based on the user's input on the screen before.
Defining custom variables is easy - you just provide a variable name where a variable name is required.
There are three places in Setup Factory where you can define custom variables:
Screen Properties dialogs
You can define variables to store the information received as a result of user input on many of the screens that you can include in your installer.
Action Properties dialogs
You can define variables using many of the actions in Setup Factory. These variables only come into effect as each action is performed.
Package Properties dialogs
You can define variables by setting up packages. Each package needs a unique custom variable that will be set to either true or false depending on whether the user selects or deselects that package.