Ok, how about this.
You're a 2 dimensional creature living on a flat plain. For you, the 3rd dimension does not exist. However, the 3rd dimension does exist, and someone has curved your flat plain into a cylinder. You can't tell, because you, light, and everything else continues to move only along the surface of the plain. But, if you travel in one direction, you end up back where you started. If your plain is curved again into a sphere, then you can travel in any direction and end up where you started.
For our universe, the flat 3d world may be curved in many other dimensions, making it closed and edgeless.
You call the surface of the sphere an edge, because for you, a 3d being, a sphere has an inside and an outside. But to mr.2d, it only ever has a surface.
Similarly, we will never see the 'edge' of a closed 3d universe, as we only ever see those 3 dimensions.