This video presents the basic definition of a vector network analyzer (VNA), a practical view of how some of the measurements are performed, and an introduction to some of the common measurements that are made. A few examples VNAs are shown. Knowledge of transmission lines, reflections, VSWR, etc. is helpful, but not required for this video. Here are several additional video links that may be helpful:
Directional Coupler videos:
   • #158: Directional Coupler Basics & ho...  
   • #196: How a Directional Coupler in an...  
Transmission lines, reflections, and standing wave videos:
   • #143: Transmission Line Terminations ...  
   • #208: Visualizing RF Standing Waves o...  
Smith Chart videos:
   • #297: Basics of the Smith Chart  Int...  
   • #275: Smith Chart: Z, VSWR, Reflectio...  
Notes from this video:
http://www.qsl.net/w2aew/youtube/what...