in webconfig file

<authentication mode="Forms">
<forms cookieless="UseCookies" 
loginUrl="~/LoginInformation.aspx" timeout="10">
<credentials passwordFormat="Clear">
<user name="Siva" password="siva"/>
<user name="joseph" password="jos"/>
</credentials>
</forms>
</authentication>

After In a aspx.cs page you have write a below coding

if (FormsAuthentication.Authenticate(TextBox1.Text, 
TextBox2.Text))
        {
            Response.Write("Hi Joseph");
        }
        else
        {
            Response.Write("Please Create account");
        }

I have tested the above one . Its working fine.