windowedMyApp/WindowedMyApp/MainWindow.xaml

<Window x:Class="WindowedMyApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WindowedMyApp"
        mc:Ignorable="d"
        Title="MainWindow" MinHeight="500" MinWidth="800" WindowStartupLocation="CenterScreen" ResizeMode="CanResize">
    <Grid>
        <Grid.RowDefinitions>
                <RowDefinition Height="100"/>
                <RowDefinition Height="250"/>
            <RowDefinition Height="100"/>
        </Grid.RowDefinitions>
            <TextBlock Text="Вход" FontSize="24" Grid.Row="0" HorizontalAlignment="Center" VerticalAlignment="Center"/>

            <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" Grid.Row="1">
                <TextBlock FontSize="24">Логин (Имя)</TextBlock>
            <TextBox x:Name="loginText" Width="250" Height="35" HorizontalAlignment="Left" VerticalContentAlignment="Center" FontSize="16"/>

            <TextBlock FontSize="24">Пароль (Фамилия)</TextBlock>
            <PasswordBox x:Name="passwrdText" Width="250" Height="35" HorizontalAlignment="Left" VerticalContentAlignment="Center" FontSize="16"/>

            <TextBlock Margin="0 20 0 0" HorizontalAlignment="Center">
                <Run Text="У вас нет аккаунта? "/>
                <Hyperlink Click="toRegisterButton_Click">
                    <TextBlock TextDecorations="Underline">Зарегистрироваться</TextBlock>
                </Hyperlink>
             </TextBlock>
        </StackPanel>

        <StackPanel Grid.Row="2" Orientation="Horizontal" HorizontalAlignment="Center">
            <Button Content="Войти" FontSize="24" Width="250" Height="35" Click="Button_Click"/>
        </StackPanel>
    </Grid>
</Window>