See also the introduction to the concept of variables.
To transclude the value of a variable, use the macro call syntax with no parameters. You can also use a $macrocall widget.
A macro snippet can contain $(name)$ as a placeholder for which the value of the variable of that name will be substituted.
A variable's value can be used as a filter parameter, or as a widget attribute. The latter supports macro parameters.
<$set name=animal value=zebra>
<<animal>>
</$set>
The \define pragma below defines a macro called tags-of-current-tiddler. The macro returns the value of the tiddler's tags field, and can be accessed from anywhere else in the same tiddler (or in any tiddler that imports it).
\define tags-of-current-tiddler() {{!!tags}}
The tags are: <<tags-of-current-tiddler>>
This example uses the backlinks operator to list all tiddlers that link to this one.
<<list-links filter:"[<currentTiddler>backlinks[]]">>