The bus-stop is on the main road outside the hotel.
Always ask where the bus is going. Bus numbers are non existent, but occasionally there is a sign in the window with the name of the final destination.
The regional buses, KTEL, reach more or less the entire island. The main bus station is in Chania town, tickets can be bought in advance at the bus station. They are also sold in some kiosks and minimarkets, in some cases advertising the availability of said item. Since there are no time tables, it is impossible to say when a bus will arrive at a certain stop along the line.
Air conditioned long haul buses drive along the north coast, to the capital Heraklion. A bus trip of ten kilometers costs around 1,50 euro. The end station for the long haul buses (the green ones) is the bus station in Chania.
From Platanias and Agia Marina, the buses leave fairly often, about twice an hour. You can go by bus to all main villages and towns on Crete, but these buses are not quite as frequent.
Ask your guide or have a look at the information board. Buy your ticket on the bus.