To get to Gournes from Heraklion Airport or the port, you can take the bus (very frequent service) or taxi, which will not cost you much as Gournes is only about 10 kilometres from the airport.
If you have your own or a rented car, take the National Road towards Agios Nikolaos and turn off at the Kokkini Hani exit. Gournes is just a short distance further along. If you miss the first exit because the sign is small and hard to spot, continue to the Gouves exit. Two hundred metres further on you will see the sign to Gournes on your left; Gournes is about 1 kilometres away.
If you are coming to Gournes from the resorts to the east, i.e. Gouves, Analipsi, Anissaras or Hersonissos, the quickest route is by the old National Road. Avoid the New National Road as you will just be driving further for no reason.