Add/Delete Items from DataContext

Add/Delete Items from DataContext

How can I add or delete items from my DataContext? This is my code:
class WallModel
{
public WallModel()
{
WallItems = new ObservableCollection<Wall>();
Initialization = InitializeAsync();
}
public Task Initialization { get; private set; }
public async Task InitializeAsync()
{
WallItems.Add(new Wall { id = 2, user = 3 });
}
public ObservableCollection<Wall> WallItems { get; set; }
}
And MainPage.xaml.cs:
public MainPage()
{
this.InitializeComponent();
DataContext = new WallModel();
lvMain.DataContext = DataContext;
}