Mike,
To get to Aghia Galini you have to take the bus to Rethymnon, get off at a place called Bale or Bali (not to be confused with a place of the same name on the N Coast of Crete) and change onto a bus coming from Rethmnon to Aghia Galini. Acutally Bale is just a taverna near the road junction in the middle of nowhere.
To get to Matala you have to go to Aghia Galini as above, take another bus going to Iraklion and get off at Festos then take yet another bus coming from Iraklion to Matala.
To get to Matala is probably as quick to go via Rethymon and Iraklion.
Greecemad.