The Round kikc is quite hard to do without practice. The basic idea is to turn out the standing foot (Otherwise you pull your groin) and swing accross like a basball bat.
The Most simple and effective target is the knee area. Use the shin or foot.
As with all the techniques, you don’t just turn the body or swing it round. You do both: Shifting the weight in whilst extending your hip and leg in.
Steve Morris has done a video on youtube talking about the whole body round kick, which I recommend you should watch.
