To enter Cambodia you do need a visa but this can be done quickly in the airport when you arrive so there is no need to worry about it in advance.
On your flight you will be given two forms to fill out (basically identical), an arrivals form and a customs form. Fill both out.
When you exit your airplane you will be directed to the visa on arrival, arrivals hall.
Outside you will be given a health form to fill out. This will be taken at the door and you will receive a yellow receipt.
Inside pick up a visa application form and fill that out (very similar to the arrivals form and customers form)
NOTE: you must have 1 passport sized photo for this application.
Next you go to the payment window. The 30 day visa on arrival currently costs $35 per person. Have the cash with you as they do not accept credit cards and I saw no ATMs in the arrivals area.
Your passport will then be passed along a line of about 5 people to be stamped and add the visa to the pages. (You can see this all happening behind the counter so do not stress about them passing around your passport).
Then the last person will double check your photo in your passport with your real face and return your passport with the visa inside.
Welcome to Cambodia!