This tutorial will guide you through the steps of visualising the output of the SAGA flow direction algorithm as a mesh with arrows using the Crayfish plugin.
Another nice way to visualise the flow direction is in the 3D Map View.
1. In the main menu go to View | New 3D Map View
2. Adjust the size of the window, but don't dock it.
3. Click to configure the 3D Map View.
4. In the 3D Configuration dialogue choose under Terrain for Type DEM (Raster Layer). Choose DEM as Elevation. Keep the other settings as default. Click OK.
5. The 3D scene will now render. Click the scroll button of your mouse and drag it slowly to the bottom of your screen. This will change the view. You can also use the buttons of the compass in the window.