Although you can dive right into this book, I recommend setting up a modest home lab of three servers running VMware ESXi and vCenter. You are also encouraged to spend time exploring the hands-on labs offered for free by VMware. The specific NSX labs that will help you greatly are HOL-1703- SDC-1 and HOL-1703- USE-2. The labs help you get started with NSX without having to worry about the intricacies of having to set it up.
You can get to hands-on labs by visiting http://labs.hol.vmware.com and searching for the two labs I mentioned previously.