Knowing the place quite well, I can't understand the map.
As you come out of the airport building, you will see a long row of wooden stalls in front of you where each tour operator has a desk. You need to go to the left of these and then walk away from the aiport building across parking areas etc. As far as I can remember there is a sort of cross-roads where the main exit from the airport is straight ahead, on the left is a periptero (kiosk) where you buy a bottle of water and on the right is the bus station (actually a tiny kiosk where you buy a ticket), a bus shelter and usually 3 or 4 buses waiting.
You have to get the local bus into Iraklion. Tell the driver you want the bus station for Rethymnon and he'll tell you where to get off. Then you have to walk for a few minutes to the bus station. Then you take a bus to Rethymnon (last year they were mostly on the half hour), then you change and take another bus to Plakias.
Greecemad