Variables are useful when you need to put some short piece of text to many places, and have a way to modify the text chunk in a centralized manner.

To achieve this, you can create a global variable through Tools > Portal Settings... > Dynamic Output > Variables or a project variable through Current Project > Variables... and assign a value to the created variables.

To use a variable in a topic, switch to the Single-Sourcing tab of the Design View, and select a variable's name in the Variables group.

When using the Source mode, use this syntax to insert a variable:

 <ch:var name="variableName" />