The guide for your walking foot enables you to keep the distances between designs uniform. Say you're doing an echo design. Put the guide on and it'll follow along your previous quilting so its even all around. :D
My walking foot has a little hole that the guide pole goes through.
The extension table will assist you with holding the weight of quilt and is a very good thing!!! As the bigger the heavier and it can become very cumbersome holding a larger object.