Astronomy cast-Observation 1

http://www.astronomycast.com/astronomy/ep-78-what-is-the-shape-of-the-universe/
This Astronomy cast was on the shape of the universe and started becoming very confusing to me near the end of it. At first, they talked about how in our universe, physics only allows for light to travel at a certain speed which allows for us to see only objects within a certain amount of light-years from the earth, somewhere around 10-20 billion light-years, since that is how old the universe is, or seems to be. Then they started talking about how the universe is flat, as opposed to open or closed. This is where I became confused with the astronomy cast and was confused for the rest of the time remaining.