Quick Start Guides for instructors and students, as well as demo videos and other resources are available here: 

higher ed: https://web.respondus.com/he/lockdownbrowser/resources/ 

K-12: https://web.respondus.com/k12/lockdownbrowser/resources/ 

You can also watch helpful installation videos:
Windows: https://youtu.be/3LlLF2j62Zw
Mac: https://youtu.be/wW8kTxzaQBs