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:
https://www.youtube.com/watch?v=iBK9ZIx9YaY
https://www.youtube.com/watch?v=byF1FLdbUiA
Transmission lines, reflections, and standing wave videos:
https://www.youtube.com/watch?v=g_jxh0Qe_FY
https://www.youtube.com/watch?v=M1PgCOTDjvI
Smith Chart videos:
https://www.youtube.com/watch?v=TsXd6GktlYQ
https://www.youtube.com/watch?v=ImNRca5ecF0
Notes from this video:
http://www.qsl.net/w2aew/youtube/what_is_a_VNA.pdf