LoginWindow/IDU/MainWindow.xaml

<Window x:Class="IDU.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:IDU"
        mc:Ignorable="d"
        Title="WindowIDU" Height="350" Width="525">
    <Grid>
        <DataGrid Name="dgogrenci" HorizontalAlignment="Left" AutoGenerateColumns="False"
Height="185" Margin="22,37,0,0" VerticalAlignment="Top" Width="246">
            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding ID}" Header="ID" Width="*"/>
                <DataGridTextColumn Binding="{Binding FirstName}" Header="First Name" Width="3*"/>
                <DataGridTextColumn Binding="{Binding LastName}" Header="Last Name" Width="3*" />
            </DataGrid.Columns>
        </DataGrid>
        <TextBox Name="txtId" HorizontalAlignment="Left" Height="23" Margin="371,61,0,0"
TextWrapping="Wrap" Text="" VerticalAlignment="Top" Width="120"/>
        <TextBox Name="txtFirstName" HorizontalAlignment="Left" Height="23" TextWrapping="Wrap" Text=""
VerticalAlignment="Top" Width="120" Margin="371,89,0,0"/>
        <TextBox Name="txtLastName" HorizontalAlignment="Left" Height="23" TextWrapping="Wrap" Text=""
VerticalAlignment="Top" Width="120" Margin="371,117,0,0"/>
        <Button Content="Insert" HorizontalAlignment="Left" Margin="371,145,0,0" VerticalAlignment="Top"
Width="120" Height="36" Click="Click_Insert"/>
        <Button Content="Delete" HorizontalAlignment="Left" Height="36" Margin="371,186,0,0"
VerticalAlignment="Top" Width="120" Click="Click_Delete"/>
        <Button Content="Update" HorizontalAlignment="Left" Height="39" Margin="371,227,0,0"
VerticalAlignment="Top" Width="120" Click="Click_Update"/>
        <Label x:Name="label" Content="ID" HorizontalAlignment="Left" Margin="303,61,0,0"
VerticalAlignment="Top"/>
        <Label x:Name="label1" Content="First Name" HorizontalAlignment="Left" Margin="300,88,0,0"
VerticalAlignment="Top"/>
        <Label x:Name="label2" Content="Last Name" HorizontalAlignment="Left" Margin="302,117,0,0"
VerticalAlignment="Top"/>
    </Grid>
</Window>