place the <$graph> widget and then define a system of equations to graph
<$graph colors='["red","blue","green"]' unitsPerTick="2" minX="0" minY="-6" maxY="6">
5 * Math.sin(x)
1/x
x*x+x
</$graph>
An alternative method is to make the Tiddler type to be text/vnd.tiddlywiki.graph.