how to do fileupload control

hi,
How to do to get file in fileupload at button click,
My code
<asp:FileUpload ID="FileUploadimage" runat="server" />                       <asp:Button ID="btnUpload" runat="server"                           Text="Upload" onclick="btnUpload_Click"  />
 protected void btnUpload_Click(object sender, EventArgs e)         {             if (FileUploadimage.HasFile)           & ...