Question exec stored proc from button

[jt_work]

i am new to using vb net (visual studio 2008) and have managed to set up a page with a drop down that retreaves info from my server. I have tried to put a datasource connection to a button in the aspx.vb page (on click) but it seems connections can only be made in the main aspx page but they run auto when the page opens, how can i attach a sqldatasource connection to a button?