Simple example with an OSM map, a marker and a popup.

examples/osm-marker-popup.js

@@ -0,0 +1,39 @@
+var map;
+function init() {
+    
+    // The overlay layer for our marker, with a simple diamond as symbol
+    var overlay = new OpenLayers.Layer.Vector('Overlay', {
+        styleMap: new OpenLayers.StyleMap({
+            externalGraphic: '../img/marker.png',
+            graphicWidth: 20, graphicHeight: 24, graphicYOffset: -24,
+            title: '${tooltip}'
+        })
+    });
+
+    // The location of our marker and popup. We usually think in geographic
+    // coordinates ('EPSG:4326'), but the map is projected ('EPSG:3857').
+    var myLocation = new OpenLayers.Geometry.Point(10.2, 48.9)
+        .transform('EPSG:4326', 'EPSG:3857');
+
+    // We add the marker with a tooltip text to the overlay
+    overlay.addFeatures([
+        new OpenLayers.Feature.Vector(myLocation, {tooltip: 'OpenLayers'})
+    ]);
+
+    // A popup with some information about our location
+    var popup = new OpenLayers.Popup.FramedCloud("Popup", 
+        myLocation.getBounds().getCenterLonLat(), null,
+        '<a target="_blank" href="http://openlayers.org/">We</a> ' +
+        'could be here.<br>Or elsewhere.', null,
+        true // <-- true if we want a close (X) button, false otherwise
+    );
+
+    // Finally we create the map
+    map = new OpenLayers.Map({
+        div: "map", projection: "EPSG:3857",
+        layers: [new OpenLayers.Layer.OSM(), overlay],
+        center: myLocation.getBounds().getCenterLonLat(), zoom: 15
+    });
+    // and add the popup to it.
+    map.addPopup(popup);
+}