Thanks for your question. The first question is very interesting, and seems to be rather technical. Oregon State University offers this overview of vitamin K, which seems to be written from a scientific point of view but explains the difference between the two, as well as giving some uses for them. However, only a doctor will be able to explain these differences in regards to what works for you and your body.

In regards to why your friends recommended you take it, this guide suggesting how to get vitamin K in one's diet also explains why it is believed to be useful for osteoporosis patients. Again, only a doctor can tell you if this is right for you or how to go about taking it.