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: https://support.respondus.com/hc/en-us/articles/4409607231003-How-do-I-install-LockDown-Browser-