Resolution is simply the number of vertical and horizontal dots that make up your screen. These dots are called pixels . The number of pixels combined with the actual size of your screen determines how much information is displayed in what amount of space. Monitor size is easy to understand, bigger monitors have bigger screens. This is the info that is always well advertised and is measured in much the same way as TVs.
Resolution is often a different story, but can actually be more important than size.
Resolution determines how much information you can see at once. The one above was set to a resolution of 640 pixels by 480 pixels and the latter was set to 832 pixels by 624 pixels. Usually larger monitors are capable of higher resolutions. As you can see the space you have to work with is determined by more than just the size of a monitor. I like to think of bit-depths as different boxes of crayons.