convert a html template to a master page
You have to do it manually. Design the master page as you want to (probably the similar look and feel as it is in HTML template - UI that fits in Master page category)
vs cant support some htmal tags(with this erroe"vs can't support xhtml 1.0.
Try and if you are unable to find the corresponding control then please try to be specific and elaborate on which tags you are facing issue with.
do i have to define menues and other controls such as buttons and login control in master page or .aspx files
I hope you know what master page is and designated for. Based on your website design, if you want to keep your login control/menus in master page you can.
Just in case, if needed, here you go and read a little about Master pages:
MSDN: ASP.NET Master Pages[
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ASPNET: ASP.NET Master Pages Tutorials[
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ASP.NET 2.0 Master Pages[
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Using the ASP.NET UpdatePanel Control with Master Pages[
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