It is super easy to do, much easier than the McDonalds site I think (at least for registering) however I did think it was interesting that the choices are limited on the English site, if you look on the Korean version then there are more options available for sides and things (perhaps it is a work in progress as I did find out it is pretty new). You can find the English order website here.
I know that you can get other pizza's delivered of course, pizza delivery is a thriving business all over the world however this is the only one I have tried so far. I ordered for the first time on Monday night just gone and it all worked out fine, you have to register by putting in your name and phone number - they will then message you a code which you enter back at the site. You then enter your address which is mostly from drop-down menus so very easy, you can either choose your building name from a list or you can write it in yourself - mine was already listed so I just used that and then there is one more free-form address line so I put my apartment number here.
My pizza came in about 20 minutes so everything worked out well, the website is very basic and it is pretty easy to follow. I did also find this youTube video about ordering with this new English site so if you want to check it out from the blog 'Kyle Living in Korea' the link to the video is here.