I learned when I was working the top of a hat. I started on a 16" circular and had to switch for the decreases. Now I rarely use them preferring magic loop for seamless projects. I prefer 32" for socks and 40" for hats because I don't like modified ml.
If you want to use DPN here's a link to an excellent sock class with great pictures for each step. I used this for my first socks.