A cheap way to get to Edam is by the Bus. The Bus leaves from the Bus Station near Central Station. If you are standing facing the Station, then its the bus station to the right. Here you will find the Buses and signs of where they are going.
For good value BUY THE WATERLAND TICKET. It lasts you a whole day covering the Waterland area. You can get on and off the bus as much as you want, as long as you keep using the "Arriva" Bus company.
The day I bought the ticket, I went to Edam, then onto Hoorn and back to Amsterdam.
You buy the ticket from the Driver as you get on the Bus, and just show to each driver at your new destinations when boarding the Bus.
Cost in 2009 was 7euro FOR A TICKET FOR THE WHOLE DAY.
There are family passes available as well.
If you are travelling from Amsterdam to Edam you have to use the bus no trains tickets are bought in ticket office at the front of the train station, you then walk through the train station following blue footprints to the otherside, the buses go from upstairs. Journey by bus takes about 30 minutesIn Edam the bus station is a 10 minute walk to town
It's very easy to go from Amsterdam to Edam. There are buses near the central train station. (But I'm not sure abuot the number) If you are planning to visit Volendam and Marken too, buy "waterland ticket". It's 6 euro and valid all day
To reach Edam by bus, you can the 110, 112, or 114 (richting/direction Hoorn).
You should first buy a "Strippenkaart," a transport ticket which you stamp by zones.