getting directions from a custom marker with google maps API

Question

i have created a map with custom marker, but I am not sure how I can allow my users to click on the marker to get directions.

    <script type="text/javascript">
jQuery(document).ready(function($) {

    var latlng = new google.maps.LatLng(51.443054, -2.077167);
    var settings = {
        zoom: 13,
        center: latlng,
        mapTypeControl: true,
        mapTypeControlOptions: {style: google.maps.MapTypeControlStyle.DROPDOWN_MENU},
        navigationControl: true,
        navigationControlOptions: {style: google.maps.NavigationControlStyle.SMALL},
        mapTypeId: google.maps.MapTypeId.ROADMAP
    };
    var map = new google.maps.Map(document.getElementById("map_canvas"), settings);
    var companyLogo = new google.maps.MarkerImage('<?php bloginfo('template_url'); ?>/images/map-marker.png',
    new google.maps.Size(100,50),
    new google.maps.Point(0,0),
    new google.maps.Point(50,50)
    );
    var companyShadow = new google.maps.MarkerImage('<?php bloginfo('template_url'); ?>/images/map-marker-shadow.png',
    new google.maps.Size(100,50),
    new google.maps.Point(0,0),
    new google.maps.Point(50, 50)
    );
    var companyPos = new google.maps.LatLng(51.443054, -2.077167);
    var companyMarker = new google.maps.Marker({
        position: companyPos,
        map: map,
        icon: companyLogo,
        shadow: companyShadow,
        title:"Fitzgraham",
        zIndex: 4,
        clickable: true
    });

});
</script>