You can plug it in either way. If you want the faster connection or hooking up to a network, Ethernet would be the best. You can hook it up via USB as it will run the same way. If you do large qty's of prints, it's best to go via Ethernet as USB may slow down the process a little. Either way, it's a plug and play set up. You install the drivers while it's connected and the OS should read it upfront.
Hope this helps.