Since it is digital copies you can buy by either chapter or volume depending on the series. I don't know if everything currently on the site is translated, never checked myself. For this one though it only has the first volume, 8 chapters, and it is about $9(US I'm guessing) though there is a sale right now so it is $5 if you could get on. There are some manga with free previews but they are only a few pages.
For payment it looks to be that you can either subscribe or buy points as you need them. The only real difference seems to be a sub will just charge you every month instead of whatever random time you chose to buy more points. Cost to point is equal, though you get a few bonus for subscribing.