Why can’t I upload an image file and display it?

I do not understand what happens from the time that a file is selected with the FileUpload control until a transferred image is displayed on a web page.  I assume that it can take quite some time for a file to transfer to the server and then be displayed back on the user’s computer.  Does this process begin once a file is selected and the Open button is clicked in the control’s browse window or when a submit button is clicked on the web page that contains the FileUpload control?  When does the user see the image on the web page?  This does not happen for me.
 
I assume that the FileUpload control does not actually cause a postback to occur and that it simply provides a response to a check of its “HasFile” status as well as providing the selected filename.  It appears that the command of: “FileUpload1.PostedFile.SaveAs(SavePath);” is what actually causes the transfer of the file to occur and that an image control can be passed the ...