LockDown Browser is a custom browser that's installed to each computer or device used by students to take an exam. Your LockDown Browser license administrator has access to the download links and instructions for Windows, Mac, iPad, and managed Chromebook devices.
If students will be installing LockDown Browser to their own Windows or Mac computers, be sure they use your institution's unique installation for this purpose (a URL can be obtained from your license administrator, or depending on how the integration was set up, a download link may be available from a LockDown Browser-enabled quiz).
iPad: See this KB article for more details.
Chromebook: See this KB article for more details.