Hi @LauraDiPietro1,
When Respondus LockDown Browser is used with a Canvas quiz, after the student clicks on the "Take the Quiz" button, the student will be presented with a notice that Respondus LockDown Browser is required and it will include a download link. The message will look something like what is provided below.

The download link will be specific to your institution. If the student is using a Chromebook, they will be directed to the Chrome web store. If the student is using an iPad, a webpage will appear with additional information and a link to download the app from Apple's App Store.
Since the download link is specific to each institution (with the exception of the downloading for a Chromebook or an iPad), some institutions will share the download link with their faculty and students, posting it in a central location for everyone to find.
Does this help you?
-Doug