King sized beds are larger. I don't know the exact demensions.
I've never been to Europe, but from what I understand, most of your beds are similar to the size we call a Full. Queens are a bit larger than Fulls, and then Kings are the largest.
Think of it this way - a double bed is like two crib widths wide. A king is like two twin widths wide. A queen falls between them. Kings and queens are usually longer than doubles and twins.
Most couples sleep comfortably on a queen bed. It is what my husband and I have at home. A King bed is even larger and has more than enough room for two people. A full sized bed (often called a double) can be a bit cramped for two adults.