Select a first destination from search (address search, POI search or your personal waypoints including history or favourites) and select 'Go To'. The unit will calculate the route from your current positions to this destination.

To add additional via points or new end points to an existing active route, select another destination, like mentioned before and instead of selecting 'Go to' select no:

'Drive before' to add the destination as a via point, or

'Add to route' to add this as a new end point. The old end point will become via point now.

You can add as much such points to the route, as you need.