ESRI -add a new point on map

[JulieBiju]

Advance tha ks to all.I am using vs2010 and silverlight 4 for developing my web application.Now my development project is going on and io am loading map with the following code.It is working fine.

<esri:Map x:Name="MyMap" Background="White" WrapAround="True">
<esri:ArcGISTiledMapServiceLayer ID="PhysicalTiledLayer"
Url="http://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer"/>
<esri:GraphicsLayer ID="MyGraphicsLayer" />
</esri:Map>

this part i added in mainpage.xaml.Now my requirement is in mainpage.xaml i added a button LnkLastPosition.When i click this button i need to show one small ball icon on map with blue colour in (58,23) long and lat values.Can anybody help me to write that code?

Here i specified 58,23 as example.This long and lat is not fixed.

After adding ball icon on map i need to add a tooltip infomation on that icon?

Please help me with vb.net code....

[DominiqueBroux · Accepted solution]

This sample : http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#AddGraphics demonstrates how to add graphic objects by code.
It's probably a good starting point for what you need to do.