how to remover aperture library from iMac to external HD?

I want to remove my complete aperture library to an external HD. Aperture program included. How do I do that?

You can simply drag and drop your Aperture library to external HD. Just make sure, that the external drive has the correct filesystem - MacOS Extended (Journaled). And the disk needs to be locally mounted, not a NAS or a network share, see this link: Use locally mounted Mac OS X Extended volumes for your Aperture library

But keep the Aperture application in your Applications folder. Moving the application to a different folder can result in unexpected behaviour, because the system will expect the application to be in the correct folder.