Bootcamp imac late 2012 support

It is not clear what you are asking. Boot Camp Assistant is already on your computer. You buy Windows from Microsoft. Follow these instructions to install Windows using Boot Camp Assistant. Boot Camp - Official Apple Support

If you have a 3TB Fusion drive, see If you see the alert 'Installation cannot proceed with Boot Camp configured' - Apple Support.

If some Mac features don't work when running Windows in Boot Camp - Apple Support.