<Window x:Class="WpfAppFontAwesome.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:WpfAppFontAwesome"
          mc:Ignorable="d"
          xmlns:fa="http://schemas.fontawesome.com/icons/"
          Title="MainWindow" Height="450" Width="800">
     <Grid>

          <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">

               <fa:ImageAwesome
                    Icon="Solid_Undo"
                    Height="18"
                    Foreground="Blue"
                    Margin="20 0 0 0"
                    HorizontalAlignment="Left"/>

               <fa:ImageAwesome
                    Icon="Solid_Table"
                    Height="18"
                    Foreground="Green"
                    Margin="20 0 0 0"
                    HorizontalAlignment="Left"/>

               <fa:ImageAwesome
                    Icon="Solid_Key"
                    Height="18"
                    Foreground="Orange"
                    Margin="20 0 0 0"
                    HorizontalAlignment="Left"/>

          </StackPanel>

     </Grid>
</Window>

xmlns:fa="http://schemas.fontawesome.com/icons/"

<fa:ImageAwesome
   Icon="Solid_Undo"
   Height="18"
   Foreground="Blue"
   Margin="20 0 0 0"
   HorizontalAlignment="Left"/>