When you create new MVC project you already have one login window/form created in application and you can find the codes inside the Views> Account Folder (for cshtml code) and similarly inside Controllers> Account controllers for controller part code and for model code you can find it in model section. You can take help of these code if you want to create your own loggin form.
In case your care not getting these files already created then you need to create it yourself.I hope it is your answer.
refer below link for getting started
http://www.asp.net/mvc[
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