I'm pretty confused. In the U.S. the meaning for the room types are as fallows:

King Size - one bed - 1 or 2 people
Queen - one bed - 1 or 2 people
2 Doubles - 2 beds - 2-4 people

In Europe it seems like they go by:
Single or Double

When you change number of people from 1 to 2, sometimes it changes the price sometimes it doesn't. Does single and double means the same as it sounds?
I mean, if you pick single you going to get one bed and only one small bed so only ONE person can sleep there or what?

Please explain.
Thank