program

using System;
using System.Collections.ObjectModel;
using System.Windows;

namespace datagridTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private ObservableCollection<Data> myList; 
        public MainWindow()
        {
            myList = new ObservableCollection<Data>();
            InitializeComponent();
            dataGrid1.ItemsSource = myList;

        }

        private void MinFinaKnapp_OnClick(object sender, RoutedEventArgs e)
        {
           myList.Add(new Data
           {
               Date = DateTime.Now,
               Name = Guid.NewGuid().ToString()
           });
        }
    }

    public class Data
    {

        public string Name { get; set; }
        public DateTime Date { get; set; }
    }
}

xaml

<Window x:Class="datagridTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="90*"></RowDefinition>
            <RowDefinition Height="10*"></RowDefinition>
        </Grid.RowDefinitions>
        <DataGrid Name="dataGrid1" Grid.Row="0" ItemsSource="{Binding Data}" AutoGenerateColumns="False" >
            <DataGrid.Columns>
                    <DataGridTextColumn Header="ID" Binding="{Binding Name}"/>
                <DataGridTextColumn Header="Date" Binding="{Binding Date}"/>
            </DataGrid.Columns>
        </DataGrid>
        <Button Name="MinFinaKnapp" Grid.Row="1" Click="MinFinaKnapp_OnClick">CLICK ME OMFGSDASd</Button>

    </Grid>
</Window>