Hello @dmc20723 
Welcome to the Canvas Community. Thanks for posting your question. I am assuming that you are a student. (If not, please let us know.) Are you using the Lockdown Browser download link that was provided to you by your instructor? You cannot just download a generic version of Lockdown Browser to your computer...as the link you'd get from your instructor is specific to your school/course. Please check with your instructor for the download link to Lockdown Browser. Then, you should be able to take your quiz/test/exam that your instructor has set up in conjunction with Lockdown Browser.
I hope this helps, Danielle. Please let Community members know if you have other questions about this...thanks!
