Code
<?xml version="1.0" encoding="utf-8"?>
<mx:Application
    xmlns:mx="http://www.adobe.com/2006/mxml"
    xmlns:esri="http://www.esri.com/2008/ags"
    layout="absolute"
    >
     <mx:Script>
        <![CDATA[
            import com.esri.ags.Graphic;
            import com.esri.ags.events.DrawEvent;
            import com.esri.ags.events.IdentifyEvent;
            import com.esri.ags.geometry.Geometry;
            import com.esri.ags.symbol.Symbol;
            import com.esri.ags.toolbars.Draw;
              import com.esri.ags.SpatialReference;
            import com.esri.ags.events.GeometryServiceEvent;
            import com.esri.ags.tasks.BufferParameters;
            private function drawEndHandler(eventrawEvent):void
            {
                var geometry : Geometry = event.geometry;
                var myMapPoint:Graphic = new Graphic();
                myMapPoint.geometry = geometry;
    geometry.spatialReference = new 
SpatialReference(4016);
                var bufferParameters : BufferParameters = new 
BufferParameters();
                bufferParameters.features = [myMapPoint];
                bufferParameters.distances = [300000];
                bufferParameters.unit = BufferParameters.UNIT_METER;
                bufferParameters.bufferSpatialReference = new 
SpatialReference(102113);
                
                myGeometryService.addEventListener
(GeometryServiceEvent.BUFFER_COMPLETE, bufferCompleteHandler);
                myGeometryService.buffer( bufferParameters );
           }
                function bufferCompleteHandler( event : 
GeometryServiceEvent ) : void
                {
                    myGeometryService.removeEventListener
(GeometryServiceEvent.BUFFER_COMPLETE, bufferCompleteHandler);
                    for each ( var graphic : Graphic in event.graphics 
)
                    {
                        graphic.symbol = sfs;
                        myGraphicsLayer.add( graphic );
                    }
                }
           
        ]]>
    </mx:Script>   
     <esri:SimpleFillSymbol id="sfs" color="0xFF0000">
        <esri:SimpleLineSymbol color="0x000000"/>
    </esri:SimpleFillSymbol> 
    <!-- Draw ToolBar -->  
    <esriraw id="drawToolbar" map="{map}" 
graphicsLayer="{myGraphicsLayer}" drawEnd="drawEndHandler(event)">
    </esriraw>    
       <esri:GeometryService id="myGeometryService"
        
url="http://sampleserver2.arcgisonline.com/ArcGIS/rest/services/Geometr
y/GeometryServer"/>    <mxanel  width="100%" height="100%">
       <mx:Button label="buffer" click="drawToolbar.activate
(Draw.MAPPOINT)"/>    
        <esri:Map id="map" width="100%" height="100%">
            <esri:ArcGISDynamicMapServiceLayer
                
url="http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Special
ty/ESRI_StatesCitiesRivers_USA/MapServer" />
            <esri:GraphicsLayer id="myGraphicsLayer"/>
        </esri:Map>
</mxanel>
</mx:Application>