Создал странциу и в окно поместил фрейм

WPF01/MainWindow.xaml

@@ -6,7 +6,8 @@
         xmlns:local="clr-namespace:WPF01"
         mc:Ignorable="d"
         Title="Вход в систему" Height="400" Width="600" Visibility="Visible" MinWidth="290" MinHeight="350">
-    <Grid Margin="0" >
+
+    <Grid>
         <Grid.Background>
             <LinearGradientBrush EndPoint="0.5,1" MappingMode="RelativeToBoundingBox" StartPoint="0.5,0" Opacity="0.2">
                 <LinearGradientBrush.RelativeTransform>
@@ -21,11 +22,18 @@
                 <GradientStop Color="#FF02C1B0" Offset="0.995"/>
             </LinearGradientBrush>
         </Grid.Background>
-        <TextBox x:Name="textBoxLogin" Margin="0,82,0,0" TextWrapping="Wrap" Width="200" Height="30" VerticalContentAlignment="Center" HorizontalAlignment="Center" VerticalAlignment="Top" Visibility="Visible" BorderThickness="10,1,1,1" KeyDown="TextBoxInput"/>
-        <PasswordBox x:Name="textBoxPassword" Margin="0,143,0,0" Width="200" Height="30" VerticalContentAlignment="Center" HorizontalAlignment="Center" VerticalAlignment="Top" Visibility="Visible" BorderThickness="10,1,1,1" PasswordChar="♦" KeyDown="TextBoxInput"/>
-        <Button x:Name="buttonLogin" Content="Button" HorizontalAlignment="Center" Margin="0,198,0,0" VerticalAlignment="Top" Width="200" Height="30" IsEnabled="False" Visibility="Visible" BorderThickness="1" Click="ButtonClick"/>
-        <Label Content="Логин:" HorizontalAlignment="Center" Margin="0,56,0,0" VerticalAlignment="Top" Width="200"/>
-        <Label Content="Пароль:" HorizontalAlignment="Center" Margin="0,117,0,0" VerticalAlignment="Top" Width="200"/>
+        
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="1*"/>
+            <ColumnDefinition Width="120"/>
+        </Grid.ColumnDefinitions>
+
+        <Grid.RowDefinitions>
+            <RowDefinition Height="24"/>
+            <RowDefinition Height="1*"/>
+        </Grid.RowDefinitions>
+
+        <Frame x:Name="MainFrame" Margin="0" Loaded="Frame_Loaded" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" NavigationUIVisibility="Hidden" ></Frame>
     </Grid>
 
 </Window>

WPF01/MainWindow.xaml.cs

@@ -23,24 +23,13 @@ namespace WPF01
         public MainWindow()
         {
             InitializeComponent();
-        }
 
-        private void ButtonClick(object sender, RoutedEventArgs e)
-        {
-            MessageBox.Show("Hello World");
+            MainFrame.Navigate(new pages.Authorization());
         }
 
-        private void TextBoxInput(object sender, KeyEventArgs e)
+        private void Frame_Loaded(object sender, RoutedEventArgs e)
         {
-           if (textBoxLogin.Text.Length >= 4 && textBoxPassword.Password.Length >= 4)
-            {
-                buttonLogin.IsEnabled = true;
-            }
-            else
-            {
-                buttonLogin.IsEnabled = false;
-            }
+           
         }
-
     }
 }

WPF01/WPF01.csproj

@@ -67,8 +67,15 @@
       <DependentUpon>MainWindow.xaml</DependentUpon>
       <SubType>Code</SubType>
     </Compile>
+    <Page Include="pages\Authorization.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="pages\Authorization.xaml.cs">
+      <DependentUpon>Authorization.xaml</DependentUpon>
+    </Compile>
     <Compile Include="Properties\AssemblyInfo.cs">
       <SubType>Code</SubType>
     </Compile>

WPF01/pages/Authorization.xaml

@@ -0,0 +1,20 @@
+<Page x:Class="WPF01.pages.Authorization"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
+      xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
+      xmlns:local="clr-namespace:WPF01.pages"
+      mc:Ignorable="d" 
+      d:DesignHeight="450" d:DesignWidth="800"
+      Title="Авторизация" Width="250" Height="250">
+
+    <Grid Margin="0" >
+        
+        <TextBox x:Name="textBoxLogin" Margin="25,50,25,0" TextWrapping="Wrap" Width="200" Height="30" VerticalContentAlignment="Center" HorizontalAlignment="Center" VerticalAlignment="Top" Visibility="Visible" BorderThickness="10,1,1,1" KeyDown="TextBoxInput"/>
+        <PasswordBox x:Name="textBoxPassword" Margin="25,111,25,0" Width="200" Height="30" VerticalContentAlignment="Center" HorizontalAlignment="Center" VerticalAlignment="Top" Visibility="Visible" BorderThickness="10,1,1,1" PasswordChar="♦" KeyDown="TextBoxInput"/>
+        <Button x:Name="buttonLogin" Content="Вход" HorizontalAlignment="Center" Margin="25,166,25,0" VerticalAlignment="Top" Width="200" Height="30" IsEnabled="False" Visibility="Visible" BorderThickness="1" Click="ButtonClick"/>
+        <Label Content="Логин:" HorizontalAlignment="Center" Margin="25,24,25,0" VerticalAlignment="Top" Width="200"/>
+        <Label Content="Пароль:" HorizontalAlignment="Center" Margin="25,85,25,0" VerticalAlignment="Top" Width="200"/>
+    </Grid>
+
+</Page>

WPF01/pages/Authorization.xaml.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Navigation;
+using System.Windows.Shapes;
+
+namespace WPF01.pages
+{
+    /// <summary>
+    /// Логика взаимодействия для Authorization.xaml
+    /// </summary>
+    public partial class Authorization : Page
+    {
+        public Authorization()
+        {
+            InitializeComponent();
+        }
+
+        private void ButtonClick(object sender, RoutedEventArgs e)
+        {
+            
+        }
+
+        private void TextBoxInput(object sender, KeyEventArgs e)
+        {
+            if (textBoxLogin.Text.Length >= 4 && textBoxPassword.Password.Length >= 4)
+            {
+                buttonLogin.IsEnabled = true;
+            }
+            else
+            {
+                buttonLogin.IsEnabled = false;
+            }
+        }
+
+
+    }
+}