Entity.cs

namespace Example
{
    public class Entity
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Address { get; set; }
    }
}

EntityViewModel.cs

using GalaSoft.MvvmLight;

namespace Example
{
    public class EntityViewModel : ViewModelBase
    {
        public EntityViewModel(Entity e)
        {
            this.entity = e;
        }
        Entity entity;
        public int Id
        {
            get { return entity.Id; }
            set
            {
                entity.Id = value;
                RaisePropertyChanged("Id");
            }
        }
        public string Name
        {
            get { return entity.Name; }
            set
            {
                entity.Name = value;
                RaisePropertyChanged("Name");
            }
        }
        public string Address
        {
            get { return entity.Address; }
            set
            {
                entity.Address = value;
                RaisePropertyChanged("Address");
            }
        }
    }
}

MainWindow.xaml

<Window x:Class="Example.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:l="clr-namespace:Example"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <l:MainWindowViewModel x:Key="vm"/>
    </Window.Resources>
    <Grid DataContext="{StaticResource vm}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="22"/>
            <RowDefinition Height="22"/>
            <RowDefinition Height="22"/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Label Padding="0,2,0,0" Content="Id" Grid.Column="0" Grid.Row="0"/>
        <Label Padding="0,2,0,0" Content="Name" Grid.Column="1" Grid.Row="0"/>
        <Label Padding="0,2,0,0" Content="Address" Grid.Column="2" Grid.Row="0"/>
        <TextBox Text="{Binding NewEntity.Id}" Grid.Column="0" Grid.Row="1"/>
        <TextBox Text="{Binding NewEntity.Name}" Grid.Column="1" Grid.Row="1"/>
        <TextBox Text="{Binding NewEntity.Address}" Grid.Column="2" Grid.Row="1"/>
        <Button Content="Add" Command="{Binding AddEntityCommand}"  Grid.Column="1" Grid.Row="2"/>
        <DataGrid CanUserAddRows="False" AutoGenerateColumns="False" HeadersVisibility="None" ItemsSource="{Binding Entities}" Grid.ColumnSpan="3" Grid.Row="4">
            <DataGrid.Columns>
                <DataGridTemplateColumn Width="*">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Label Content="{Binding Id}"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
                <DataGridTemplateColumn Width="*">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Label Content="{Binding Name}"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
                <DataGridTemplateColumn Width="*">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Label Content="{Binding Address}"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

MainWindowViewModel.cs

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using System.Collections.ObjectModel;

namespace Example
{
    public class MainWindowViewModel : ViewModelBase
    {
        public MainWindowViewModel()
        {
            Entities.Add(new EntityViewModel(new Entity() { Id = 1, Name = "Jeniffer Glasgow", Address = "3, Main Road" }));
        }
        /// <summary>
        /// The <see cref="NewEntity" /> property's name.
        /// </summary>
        public const string NewEntityPropertyName = "NewEntity";

        private EntityViewModel ne = new EntityViewModel(new Entity());

        /// <summary>
        /// Sets and gets the NewEntity property.
        /// Changes to that property's value raise the PropertyChanged event. 
        /// </summary>
        public EntityViewModel NewEntity
        {
            get
            {
                return ne;
            }

            set
            {
                if (ne == value)
                {
                    return;
                }

                RaisePropertyChanging(NewEntityPropertyName);
                ne = value;
                RaisePropertyChanged(NewEntityPropertyName);
            }
        }

        private ObservableCollection<EntityViewModel> enitites = new ObservableCollection<EntityViewModel>();

        /// <summary>
        /// Gets the Entities property.
        /// </summary>
        public ObservableCollection<EntityViewModel> Entities
        {
            get
            {
                return enitites;
            }
        }
        private RelayCommand addcommand;

        /// <summary>
        /// Gets the AddEntityCommand.
        /// </summary>
        public RelayCommand AddEntityCommand
        {
            get
            {
                return addcommand
                    ?? (addcommand = new RelayCommand(
                                          () =>
                                          {
                                              Entities.Add(NewEntity);
                                              NewEntity = new EntityViewModel(new Entity());
                                          }));
            }
        }
    }
}