<Window x:Class="WpfApp1.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:WpfApp1"
     mc:Ignorable="d"
     Title="MainWindow" Height="450" Width="800">

     <Grid>

          <Grid.ColumnDefinitions>
               <ColumnDefinition Width="*" />
               <ColumnDefinition Width="*" />
          </Grid.ColumnDefinitions>

          <StackPanel Grid.Column="0" Grid.Row="0" >
               <TextBox Text="Hello! Good bye!!!" />
          </StackPanel>

          <StackPanel Grid.Column="1" Grid.Row="0" >
               <Button>Add Text</Button>
          </StackPanel>

     </Grid>

</Window>