There's two ways to do this, one within Eclipse when you're coding/debugging/testing etc and one via Maven.
Right click the sheepdogcukeplugin project then select Run As > Eclipse Application. It should start another Eclipse Instance.
The plug-in is in the .repository directory, it's the zip file. Install the plug-in in Eclipse by selecting Help > Install New Software > Add > Archive > Open > Add > Select All > Finish.