Add below html content in your aspx page
<asp:FileUpload id="FileUploadControl" runat="server" />
<asp:Button runat="server" id="btnUpload" text="Upload" onclick="btnUpload_Click" />
protected void btnUpload_Click(object sender, EventArgs e)
{
if(FileUploadControl.HasFile)
{
try
{
string filename = Path.GetFileName(FileUploadControl.FileName);
FileUploadControl.SaveAs(Server.MapPath("~/") + filename);
}
catch(Exception ex)
{
}
}
}