If you meant ‘how do I use an arrow marker on a <line> element?’ then here’s how you do that:
<line x1="100" y1="230" x2="300" y2="230"
marker-end="url(#yourMarkerId)" stroke="black" stroke-width="10"/>
Here’s a full example. And note that marker-end is a css property, so you can also put that part in a stylesheet if you want.
If you meant you want to draw your marker with lines, then just add whatever lines you need as a child of the marker element (and make sure to use the coordinate system defined by the marker’s viewBox attribute).