You can add lines to the plot in the QTopo drawing windows. Lines are drawn as sequences of points: they are just like centerlines and you mark all the stations in sequence to draw them.
Only a few Therion line types are supported and there is only a limited support for their options.
Furthermore centerline shot are red.
Splay shots are black. To display them
use the Splay toggle button.
In Line insert mode the Mode button shows a pencil, and the cursor is a pencil. It is vertical before you start drawing, and turns slanted while you draw the line. Lines are drawn as consecutive segments: you click on the points in sequence. To finish the line click a second time on the last point. You finish a line also be clicking on its first point; this way you get a closed line. A line is automatically finished if you switch mode, or change line type.