I would like to know what they mean, and how can I use them.
By default, InstallBuilder installers use a set of installer environment variables. These variables contain data for the installation project that will be substituted for their values at runtime. You can set and read all of the installation parameters using installer environment variables. For example, if you display the following text in one of the installer's page:
The software will be installed in ${installdir}
if the user selects "/opt/installbuilder" as the installation directory, then the text will be rendered as :
The software will be installed in /opt/installbuilder
You can find the complete list of the default installer environment variables and their meaning in the Advanced Functionality section of the product documentation included with InstallBuilder. Installer environment variables are not related to the system environment variables. Those can be accessed using the ${env(varname)} construct, as explained below.