uploading a file

I wonder if someone can help me with some coding and advice, I am very new to this and am a bit lost.  I have a form that I would like the users of my website to use and to be able to have the option to send me a .doc or .pdf file.  Now I have read that the best way forward would be to have the file stored in a file on my website not on the database but I have absolutely no idea how to go about this.  I know this is probably a big ask but can anyone help me with this?  The page currently has this code:
 
 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <%@ Page Language="C#" %> <html dir="ltr" xmlns="http://www.w3.org/1999/xhtml">
<head runat="server"> ...