You can use DockPanel to arrange your controls. like this Toolbar will be dock at top, Statusbar at bottom and rest space will be assigned to datagrid because we have set the "LastChildFill" to true in dockpanel.
<Window x:Class="MyApp.MyForm"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MyForm" Height="346" Width="459">
<DockPanel LastChildFill="True">
<ToolBarTray DockPanel.Dock="Top">
<ToolBar>
<Button Command="Edit" Content="Edit" />
<Button Command="Delete" Content="Delete" />
<Button Command="Refresh" Content="Refresh" />
</ToolBar>
</ToolBarTray>
<StatusBar Name="statusbar" DockPanel.Dock="Bottom">statusbar</StatusBar>
<DataGrid Name="grdEmployees" ItemsSource="{Binding EmpCollection}" />