The high-key setup is a little bit more difficult to achieve, but if you follow the simple rules Marc gives in this video, everything should be fine.
"High-key" basically means that the background will be illuminated with a light. Thus, one flash head is going to be fully dedicated to the back so that it becomes white.
The easiest is to place this light behind your subject so that it's directed to the back.
The second flash head will be the main light for the subject.
And never forget, photography is only a fun experiment. You have to play with light, try different settings and make mistakes in order to fully understand and master this "photographic science".